Sorry to hear about your injury! If you have access to a pool, interval swimming might be just the thing. Few people whom I’ve met apply interval training to swimming, but the clients to whom I’ve recommended it love it. A simple example, swim three lengths at a moderate pace, then go as hard as you can for one length. Repeat the pattern, allowing yourself to recover during the three easier laps. The most obvious benefit, in your situation, is that you need not be on your feet, nor do you need to kick. (although some modest kicking can help aid in maintaining ankle mobility during the healing process) Additional benefits are increased oxygen usage, improved cardiorespiratory function, and excellent usage of your abdominals and latissimus (if using a crawl stroke).
Best wishes for a speedy recovery!