Dull, but delightful
Solution 1:
Possibly 'Anodyne'
The OED gives
Having the power of assuaging pain
fig Soothing to the mind or feelings.
and adds a Draft Addition dated March 2007 of
Unlikely to provoke a strong response; innocuous, inoffensive; vapid, bland.
It seems to me that in common use and in the situation you suggest the meaning would be somewhat of a mash up of the figurative and draft additional definitions, bland and unexciting, but producing a beneficial mental effect.