hi there, i dont know if overs appear bigger than unders that im sure pretty much is somthing to do with what size you are and what size implant you have had?
But overs look more fake and unders natural. Unders take 6 to 12 months for the muscle to fully heal, but by all accounts you should feel fine after 6 weeks. where as with overs 6 weeks and all done, there abouts.
and im sure you will sleep on your front again, once all healed. and yes nipple sensation is lost post opp but should return slowly but as with any opp in that area there is always a chance it will never return fully or at all or they can become too sensitive. are you post opp? and are you unders or overs ?