Hmm, my husband and I were actually quite worried about this as well when we first bought our son home three months ago. However, the only way he fell asleep in the beginning was to sleep on our chests. However because I am a fitful sleeper at night and can't stand sleeping on my back....my husband sleeps with him every night on the couch with our son on his chest.
The majority of the time Damien(our son) just sleeps better on his belly on someone. Hell, I've been more worried about putting him on his back in his crib because of his tendency to roll all over since he was born. Then he thrusts his legs to pivet his body in such way that his head will end up in the matress. -.- Very active like me at night.
Anyway, the co-sleeping arangement is not only the easiest one for us, it's also still safe. He moves and whines if he's too warm or cold and my husband will wake right up and adjust for him. He wakes right up if damien shifts too much so it's quite comfortable.
And it gives me a break from holding him day in and day out. I get to sleep on my side in a nice soft bed and take a little break. Feel bad for saying that. I still worry about SIDS and proberly will until he reaches about 3 1/2 years old...so do what works best for you. ^-^
Im not crazy...just eccentric and mildly insane at moment. Oh...I just fudged that didnt I? -.-