I was a belly sleeper (still am!) right up until the night before I had my c/sections. I would just sleep with two pillows under my head (three towards the end) a pillow under my chest (2 towards the end) and just added others in places taht made me feel comfortable!
My last bub was 13lb 2oz and I was carrying 6 litres of fluid, so as you can imagine ... I was huge! Bub was also incredibly active and as I spent 6 ½ weeks in hospital before he was born, the midwives would stand by my door and watch me bounce up and down in my sleep as bub moved about!
Just find a way to make yourself comfortable ... doesn't matter how silly it looks ... and get plenty of sleep!