Have you checked into Road Runner cases? They're sort of a cross between a regular case and a gigbag. I know they sell them at Guitar Centers. I'm not sure if any other retailers stock them, but a quick search could tell you. The ones I'm thinking of are rectangular, with a loose nylon covering but still attached on all sides if that makes any sense. They have form-fitted, covered styrofoam interiors, so they're really lightweight compared to a regular hardshell case, but they still provide some good protection.
I'm disabled too, so sometimes I have a rough time with a heavy case. Good luck in coming up something that works for you.
Goldtop