I have rather weak feet in that i can do an extended boxing workout/jogging about 3 times a week, but i need at least a days rest in between or my ankle become sore/hurting/whatever. I think it's because i've had an injury there a few years ago... in the ring i'm a mover, so this is a vital part of my game. Swimming is a good alternative that is easy on the joints. Any other suggestions?
Biking would probably be up your alley. I don't notice much strain on the ankles when pushing through the peddles.
Theres something coming on the Market mid September that should solve the Problem, Running without Impact :good
Also forgot.. if you have a gym membership, there are low-impact cardio machines called ellipticals. I personally don't like them but that could be another solution for ya.