Look seriously at trikes. I have a Sun EZ-3 AX that I bought after ruining my knee falling off my mountain bike.



It's heavy (about 50 lbs.), but it's got a good gearing range...much like a mountain bike. And you can go as slowly as you need to up hill, and you won't fall over. The lowest gear is about like walking. It's kinda high, so it's easy to get on and off it, and you're looking at automobile drivers about eye-to-eye. I think two-wheelers are more fun to ride, but it's not bad.