I am interested in hearing about this, too.
I am not disabled, but my knees are pretty trashed now. I ride a tall horse, so when I get off, I kind of go forward on my belly, over his neck, grap some mane in one hand, roll my right leg over the rump, keep my tummy over the saddle and take my left foot out of the stirrup, then holding on tight to the cantle , I LOWER myself down slowly. I dont' drop down to the ground, because my knees may buckle, but use the saddle to lower myself down slowly, and from a 17hh horse, that's a ways!
I do hope you can get back in the saddle and admire your drive to make it work!