Im a back sleeper as well...theres nothing wrong with laying on your back as long as your not on it 24/7 ..atleast thats wat my doc says...youll know when its time to stop bc it will get so uncomfortable and difficult to breath...I swap out from my back to my side ...
Try shoving a pillow behind your back when you lay on your side so that you can't flip over. It's better to sleep on your left side so I would suggest laying on that side to begin with. I'm a stomach sleeper and would flip without knowing it, the pillow helps me stay on my side.