I have a u-shaped pillow and another pillow thats 2 small wedges with a strap between them to support my back and belly. I use them together and it's really comfy and I don't roll on my back.
It's shaped like your drawing but I use the piece you tuck behind your back between my knees
I’m a really bad back sleeper. I normally take an extra pillow or even a comforter and stuff it under one hip and thigh and that seems to help me not toss and turn as much. I adjust to where I’m kinda sideways but not fully on my side