I have a speedbag at home for when I am just not feeling like lower body cardio. You can pick up a speedbag rack for under 100$ and it is a great investment. It improves coordination and can get your heart going pretty decently.
You could also get a pull-up bar installed in a doorway. Try to use as many muscles as possible without impacting your ankle.
Leg Lifts, Situps (if you can), 1 legged push-ups with a clap. Bicycle crunches utilize a lot of muscles and have zero pressure or impact on the ankle.
Just some ideas out there for you, but you are ultimately the one that will make the difference between unable to do cardio, and unwilling to do cardio. You can give someone all the tools in the world, but ultimately it's up to them to really WANT to make themselves better.