Look up loop resistance bands, they’re very light on joints compared to weights and are in fact used for rehab but as effective as weights. I use the Weller App for workouts.
Read up/watch videos for simple beginners Pilates - it was originally developed for people recovering in bed from war injuries. Good luck with your journey. <3
I just typed exercises in bed in YouTube and so many videos and rehab ones - I would start there. You can learn the suggested moves and do them when you like, but I am more motivated to follow a video to its conclusion and feel like I’ve accomplished something.