Running out of exercise options!

Have stalled Total Knee Replacement for years with instaflex. Knee is very stiff but not painful. Now my hip is starting to get almost as bad. Age is not for sissies! I have stopped running and gone to Stationery Bike, light Cal, and walking. Now walking and bike are starting to raise havoc with my hip. What's left to keep the fat and excess weight off???? Your thoughts please.