Chronic pain making sex very limited

For reference, I am a trans man. My girlfriend is a trans woman. We both have our “original parts”. As long as I have been having sex, it had been extremely painful. Like, feels like I’m being split apart painful. For years, I either didn’t engage, or would have to stop during because I was in agony. Ever since I moved out, for the first time in my life, I can have sex with little vaginal pain. I have chalked this up to me being able to relax (no worries of getting walked in on, or having to be cramped in a car). However, I still have considerable pain everywhere else (because I have chronic pain and have it 24/7 lol). Because of this, the only position we’ve found that works is missionary. I have fairly moderate back pain, so I can’t arch my back at all, and I can’t be on my knees for too long without them hurting. Basically everything hurts, and all I can do is lay there. My girlfriend, bless her heart, has been very accommodating and understanding when it comes to this. I just don’t want her to ALWAYS have to be the one on top doing all the work. Has anyone else experienced something like this? Are there any products (i.e cushions) that would help, or sex positions? Stretching more would probably help, lol. Thank you all very much.