When I used to have a cat, at the time I usually slept on my side but I'd switch sides occasionally. She'd be sleeping right on my hip/butt. If I wanted to roll over, I'd just shift a bit first to warn her, then just roll over a bit more slowly than normal and she'd either just jump off while I moved or sometimes just stay on me like a slow rolling log walk. Then, once I'd settled, she would do the same, unless she felt like she was needed at the window or something.

We kinda trained each other... Sorry, cat, but I need to switch sides from my side, claws if I moved too quickly from hers (not because she was pissed at me but to help keep her footing), but it didn't take long to sync up with each other.