My ob actually told me to sleep however I was comfortable. Back or side or tummy. Every ob is different though.
After i got big and was not able to breathe that well and it hurt to lay on my back it was easy just lay on my side. I didn't start sleeping on my side until I was about almost 30 weeks with my first maybe a little after.
Pillows behind you to wedge you
Pillow between my legs went a long way! 😩