'Which', 'whose' or something else?

I would appreciate your help phrasing the following:

I am looking for elements which/whose/... size/sizes is/are relatively large.

Whose is the way to go here. Merriam-Webster defines it as follows:

of or relating to whom or which especially as possessor or possessors

Which wouldn't work, because it doesn't indicate possession. It would work, however, if the phrase read:

I am looking for elements which are relatively large (in size).

As to the "size is" vs "sizes are", I would say that both are grammatically correct, though the singular is preferred. The Google stats look as follows:

• "are * whose sizes are" — 94,700
• "are * whose size is" — 1,020,000

Searching the British National Corpus returns four results for "whose size is" (one of which is actually used with a plural noun, "segments whose size is"), but none for "whose sizes are".

Indeed, whose is the (only) correct possessive form, for both animate (sentient) and inanimate objects.

The Wikipedia page supports this.

In addition, the possessive version of the non-sentient pronouns is the same as that of who: whose takes this role for all of them. E.g., "I will have to fix the car whose engine I ruined".