Sex with a bad knee

So I busted my knee a couple of months ago and I'm waiting for ACL surgery. As a result, I can't fully bend my knee, cause it's painful, same with applying pressure on it. I recently started having sex with a new guy, and missionary gets kind of boring after a while, for me too, not just for him... I tryed getting on top, but it's painful for me, and he gets exhausted from doing all the "work"... I jokingly suggested he needs to go to the gym to improve his endurance... But truth is I fear my limitation will make him loose interest in the relationship cause it's really new and I think a relationship with bad sex is doomed... Any advice from someone with similar problem? Positions I can try?