Safe, small exercises

Hey guys. I’m bedridden with long Covid and have been in bed for 15 months. My symptoms are relatively low, (as long as I don’t do anything) so I want to start a tiny bit of physical therapy under the guidance of a physical therapist and also with caution not to put myself into PEM.

I haven’t walked in 15 months. I can move around in bed, and get up onto my knees in bed if I have to (but that causes PEM). I can stand up very briefly, but that also causes PEM. I am wondering where you guys started and if you have any sources for small exercises that I can tailor for myself.