Recovery and fitness

Anything non impact i'm guessing would be your friend while recovering your atrophied muscles. Cycling and a cross trainer seem like the most obvious choices.

Also you could try aqua jogging. it looks ridiculous but supposed to be very good.

Also to add, any pain and stop as you don't want to injure yourself again and the general rule of thumb with running when increasing mileage is no more than 10% per week. I wold assume the same would apply here

You could add some sitting core work. You'll burn some calories, and building up your core always helps a lot of other things. I'm "pre-habbing" before getting back into running this spring, and core work is a major part of my workout routine. Most positions in Pilates floor work require no weight on your feet at all. Plus, Pilates helps build strength, balance, and flexibility. If you haven't done Pilates before, you'll want to start with a trained instructor (like a class) or do some research into proper techniques so you can get the most out of a workout. With the experiences I've had in beginner Pilates classes, I think you'd be fine if you tried a class and told the instructor about your ankle so they'd know how to help you adapt any positions that might give you trouble.