Hello mate, I have to say, huge respect to you, for what you do, and the humble, positive and hardworking attitude you’ve maintained. Legend.
I was paralysed on my left side after a brain haemmorhage, couldn’t walk, fortunately I was able to re-learn after a few years so our situations aren’t really comparable, but i did once know your pain.
There is a guy i’ve seen training in gyms in my town before, with a big upper body, who has a wheelchair. One thing I saw he had, was a kind of harness, where he strapped to a bench when pressing or whatever. This must have helped, he put up some heavy weights! I guess it was serving the same purpose as pushing your feet through the floor, providing a steady base to transfer force through. Maybe you could find one
All the best