Solution 1:

Christine Ammer, The American Heritage Dictionary of Idioms, second edition (2013) has this entry for "bed of roses":

bed of roses A comfortable or luxurious position, as in Taking care of these older patients is no bed of roses. This metaphor first recorded in 1635, is often used in a negative context, as in the example.

As the question poster notes, metaphorical (or at least figurative/symbolic) use of "bed of roses" goes back considerably farther than 1635.


Instances of 'bed of roses' in sixteenth-century English texts

Marlowe was certainly not the first English writer to use the phrase "bed of roses." From John Heywood, "A Rose and a Nettill," in An Hundred Epigrammes (1550):

What time herbs & wedes, & such thing{is} could talke, / A man in his gardeyn one daie did walke / Spiyng a nettill greene (as Themeraude) spred / In a bed of roses lyke the Rubie red. / Betwene which two colours, be thought by his eie, / The greene nettill did the red rose beautifie. / How be it he asked the nettill, what thing / Made hym so pert? so nie the rose to spryng.

A bed of roses in this instance is evidently simply a flowerbed occupied (almost) entirely by roses.

From an epistle of Seneca, in a 1576 translation Philippe de Mornay, The Defence of Death Contayning a Moste Excellent Discourse of Life and Death:

We must therby consider y• against all kindes of dart{is} & enemies, there is nothing more conuenient then not to make any account of death, wherin eche man douteth to finde some terrible matter whiche offendeth the mindes and quaileth the courages of those who naturally are indued with a self looue. For otherwise we néed not to prepare and seeke to frée our selues from the thing whereunto we should willigly of our owne mindes hasten, as vnto that that is our owne conseruation. Certainly no man learneth how in time of néed to lye vpon a bed of Roses, but rather how he may strengthen him self against torments, lest if the case so requireth he should vt ter any thing contrary to his faith or promise.

The bed of roses in this case is presented as something to lie in—presumably not a flowerbed of rose bushes or a pallet composed of bundles of stemmed (and thorned) roses, but rather a collection of rose petals—soft, delicate, and fragrant.

From Thomas Cooper, Thesaurus Linguæ Romanæ & Britannicæ (1578):

Rosárium, rosarij, n. g. Pli. A rosier: a garden, or bed of roses.

This instance is significant primarily in presenting a nonliterary instance of "bed of roses" in English in 1578 as a common descriptive term.

Froim John Foxe, Actes and Monuments of Matters Most Speciall and Memorable, Happenyng in the Church, volume 2, part 1 (1583):

At whose [James Baynham's] burning here is notoriously to be obserued, that as he was at the stake in the midst of the flaming fyre which fire had halfe consumed his armes & legs, he spake these wordes: O ye Papistes, behold, ye looke for miracles, and here now you may see a myracle, for in this fire I feele no more paine, then if I were in a bed of Downe: but it is to me as sweet as a bed of roses. These words spake he in the middest of the flaminge fire, when his legges and hys armes (as I sayd) were halfe consumed.

The "bed of roses" appears immediately after a reference to a "bed of Downe," and both refer to how the martyr is experiencing the fire in which he is being burned to death—evidently because he sees his life passing away and his soul moving toward heaven. This may be the first truly metaphorical use of "bed of roses," since it involves neither a literal flowerbed of roses nor a fanciful promise to construct a bed of rose petals as a love nest or an image of lying luxuriously in such a bed.

From Edmund Spenser, The Faerie Qveene (1590):

Vpon a bed of Roses she [an enchantress] was layd, / As faint through heat, or dight to pleasant sin, / And was arayd, or rather disarayd, / All in a uele of silke and siluer thin, / That hid no whit her alablaster skin, / But rather shewd more white, if more might bee: / More subtile web Arachne cannot spin, / Not the fine nets, which oft we wouen see / Of scorched deaw, do not in th'ayre more lightly flee.

Here, as in Seneca's epistle, the bed appears to be a bed of rose petals for the enchantress and er paramour to lie in.

From Thomas Lodge, The Famous, True and Historicall Life of Robert Second Duke of Normandy (1591):

Editha (by deuine ordinance) was that day attired, as if she intended to wooe Lucina to graunt a Sonne, and winne the Norman Duke to get a Sonne. Her hayre, in stead of gould to grace it, was goulden exceeding gould, more finer than the thrid wherewith Arachne wrought her loombe, more softer than the bed of Roses, wherein ye Morning playd with Cephalus. Bound it was after a carelesse manner, as if disdayning that so rare beauties should be imprisoned, but pleyted in such sort, as if Nature should make a laborinth for Loue, Loue could not wish a sweeter laborinth.

Cephalus is not a character in this narrative but a figure from Greek mythology, famous for an affair with Eos (the dawn goddess, represented here as Morning), which in Lodge's telling involved enjoying each other's company in a bed of roses.

From Richard Barnfield, The Affectionate Shepheard Containing the Complaint of Daphnis for the Loue of Ganymede (1594):

A paire of Kniues, a greene Hat and a Feather, / New Gloues to put vpon thy milk-white hand / Ile giue thee, for to keep thee from the weather; / With Phoenix feathers shall thy Face be fand, / Cooling those Cheekes, that being cool'd wexe red, / Like Lillyes in a bed of Roses shed.

Here a flowerbed of roses is clearly the intended meaning of "bed of roses."

From William Burton, Conclusions of Peace, Betweene God and Man Containing Comfortable Meditations for the Children of God (1594):

For want wherof [the correcting rod of God] the sonnes of men are most miserable, when they seem to be most happy, their aboundance seemeth nothing, their libertie is bondage, their peace is warre, their rest is sorrowe, their health is sicknes, and their life is death. Their laughter is but from the teeth outward. Their feasts are like the feasts of Balthasar, and their honour is like the honour of Haman. They feare any thing but not sinne, they loue any thing sauing God, they ioye in euery thing, so it be not goodnesse, like the swine which had rather wallow in the stinking puddles of mire, than in a sweete bed of Roses.

The criticism of swine for preferring to wallow in stinking mire in a sweet bed of roses seems oblivious to the thorn issue—unless, again, he imagines a bed of rose petals only, which is not an option that most swine are ever offered.

From T. Cutwode, Caltha Poetarum: or The Bumble Bee (1599):

The bird now taken from her golden locks, / faire Caltha is desirous of the Fly, / And takes the Bee, and puts him in a box, / and cals for hony for him presently, / And makes his bed of Roses by and by: / And Marygolds with pillowes of the Dasie, / That he might lie full lither and full lazie.

Since this bed is for a bee, we may suppose that flower petals would suffice for it.

From John Weever, Epigrammes in the Oldest Cut, and Newest Fashion (1599):

I neuer lay vpon a bed of Roses, / Twixt Beauties lips entombing of my tong, / Smelling rose-waterd odoriferous Poses, / Pleasing my mistris with a Mermaides song. / Of amorous kissing more then loue-sicke lauish, / Whose iuice might make my words the Readers rauish.

The image is once again of a bed of rose blossoms for sleeping or dallying in.

And from Marlowe's poem in William Shakespeare, The Passionate Pilgrime (1599):

Liue with me and be my Loue, / And we will all the pleasures proue / That hilles and vallies, dales and fields, / And all the craggy mountaines yeeld.

There will we sit vpon the Rocks, / And see the Shepheards feed their flocks, / By shallow Riuers, by whose fals / Melodious birds sing Madrigals.

There will I make thee a bed of Roses, / With a thousand fragrant poses, / A cap of flowers, and a Kirtle / Imbrodered all with leaues of Mirtle.

In Marlowe's image, as in many of his predecessors', the bed is to be composed only of the blossoms or petals of many, many roses.


Conclusions

In sixteenth-century English writing, "bed of roses" appears in two contexts: as a standard way of say a flowerbed occupied by rose bushes, and as a fanciful bed of rose petal or rose blossoms—but no thorny stems—used as a symbol of luxury, daintiness, and (in some cases) sensual delight. The latter sense frequently arises in situations where the meaning can be taken as figurative, but the phrase still strongly attaches to the image of a literal bed of roses. Indeed multiple English writers of the seventeenth century point to figures from antiquity who slept on beds of rose petals, taking it as a symbol of extreme self-pampering.

Idiomatic use of "bed of roses" to mean simply means something wonderful or a source of great pleasure or comfort does not appear (except, arguably, in the 1583 instance from Foxe's Martyrology).

Such usage does appear in the seventeenth century. For instance, John Collinges, The Spouses Hidden Glory, and Faithfull Leaning upon her Wellbeloved (1646) has this clearly metaphorical instance, where the grave is equated with a "bed of roses":

The spouse of Christ goes downe to the grave as willingly as the sleepy body goes to bed; Indeed this virgin hath cause to go willingly to it, she goes but to see where her Lord lay; It was her Bridegroomes bed, She loves the winding sheet ever since it enwrapt her Saviour; The grave is a bed of roses to her, ever since, and she cries out, I desire to be dissolved, and to be with Christ, which is best of all; ...

And from Robert Dixon, [*The nature of the two testaments, or, The disposition of the will and estate of God to mankind for holiness and happiness by Jesus Christ (1676):

Lectulus respersus floribus est bona Conscientia: A good Conscience is a Bed of Roses. And upon this Bed, this Pillow will I rest my head wea∣ried with cares and griefs, and there will I sleep secure. ... This is the reward of all my labours in the way of Holiness, that I have peace within.

Even later are instances of negative settings for "bed of roses," which (as Ammr observes) are quite common today in the form "X is no bed of roses." One of the earliest instances of such usage appears in Anonymous, The Cave of Neptune (1784), which includes the following couplet:

'No bed of roses this,' the Inca cried, / When on the burning grill he groan'd and died.

followed by this explanatory note:

The ingenuity of a priest, one of the sanguinary associates of Pizarro, a Spanish officer, contrived a gridiron for the express purpose of converting the Peruvians. The Inca and his minister were the first to be condemned to the flames; when the latter, possessing less fortitude than the former, and calling on him for aid, received this EMPHATIC answer: "Do you think that I am on a bed of roses?"