I'll be 17 weeks tomorrow but I haven't been able to lay on my stomach without at least my arm under me for the last few weeks. As long as you're comfortable or can take pressure off if you're uncomfortable you're fine.
I'm the same as spraklepea - I have always fallen asleep kind of between my side and belly. It is still comfortable for now - but I have a feeling it might not last too much longer!!!
I use a pillow as a prop and do kind of a side/belly position. I have slept like this for as long as I can remember. I can no longer lay flat on my belly on a firm surface. One hip bone no longer touches the ground and I find it uncomfortable! I did dig a small depression in the sand so I could lay and tan comfortably!!
Re: Thoughts about laying on belly
Preg #1 - PTL @ 23.5 weeks - angel in heaven (Addison Margaret)