Getting healthy for many of us means gaining weight. To lose weight is relatively simple. Decrease calories and increase exercise. It's the only way. I have lost 25lbs since surgery and could use to lose another 5-10. I do aerobic exercise 6 days per week and try to watch what I eat. Weight Watchers can be a great place to start with a structured program.
I don't have an ostomy any longer; I have a jpouch. However, I am sure you can try things to improve your seal for exercise. I have heard that wearing an ostomy belt helps as well as Eakin seals. Maybe post a question to this on this board for advice.