I wouldn't worry. The baby is surrounded by all the fluid and our own body fat. I used to sleep on my stomach until I was 35 weeks and no harm was ever done. Unless you have a hard kick or fall of some sort to your belly it's unlikely anything will actually harm the baby while in the womb.
I usually put a pillow between us, but im sure he moved it cause it was under his head lol. I was so worried i wanted to smack my husband lol.
I think You might just be over reacting as You are worried about his/her health. If Your husband moves around in his sleep a lot perhaps putting a pillow against Your stomach when You sleep might help You sleep better without worrying