Thanks so much for your replies.
The reason I asked was that the only comfortable place for me to lay is on my back. My little bubbas in the breech position and has started to lift my diaphragm and stretch my muscles beyond belief. So I have constant pain under my BBs. By night time all my ribs at the front and back feel like there bruised and when I lay on my side I feel like they're going to break.

So I'll try propping a pillow / doona under half of my back so I'm tilted to the side. Dont want to be cutting off blood flow or anything else like that.

Thanks again