Help for a back sleeper

I'm 33 weeks so definitely should not be sleeping on my back at this point. But I was a back-sleeper before and apparently my body just defaults to that no matter what I do. I fall asleep on my side now but every night I wake up laying on my back at least once and sometimes more often. I always roll to my side if I wake on my back but I'm starting to worry I'm hurting the baby. I use a body pillow on either side of my body to try to ensure even if I roll on my back, I'd be propped on an angle...but I usually wake up and find I've tossed the pillow in the floor in my sleep so it doesn't help...and the few nights that I dont toss it and wake up with the pillow wedged under my hip, I end up being in a lot of pain the next day from the angle. I just don't know what to do. Can I sleep on my back if I'm propped up on a wedge pillow? or should I buy one of those U-shaped body pillows?