Talk to your doctor and a dietician. You might also try exercising in a pool. Swimming, water walking, aerobics; water holds 15% of your body and at the same time cools you, this translates into your body not being strained as much, yet you work harder. Bouncy takes weight off your joints, your heart works easier, and you stay cooler, yet because water is thicker than air you work harder in a better way than those rubber band things, weights, etc.

Good luck!