Working with a personal trainer would also help - there are many that specialize in weight loss with those that have chronic diseases. This would give you someone that knows your weak points and how to strength, at the same point gives you motivation and can watch for signs that you are over doing the exercise.
Most major gyms or community centers will have personal trainers available. It really lets you get the most out of your workouts to get the largest level of weight loss possible. A dietican may also be available through the gyms which would be of benefit as well for you.
Good luck!
Walking would be a good place to start. You can start out for short periods of time and increase your distance and pace over time. If you walk outside, be mindful if you have allergies to trees/pollens/weeds. Do you have exercise-induced asthma? If so, you may need to use your rescue inhaler prior to exercising.