I think gentle exercise makes just about any physical malady better. There is a very gentle yoga class offered on PBS that just about anyone should be able to do. You can do it sitting in a chair and then it moves to gentle mat work, but you can do the whole thing sitting in a chair. Walking remains the best exercise -- if it is hard, shorten your stride. Take a shorter walk, as tolerated...then try to go the distance a couple times per day...even if it is a block and back.
Our bodies are designed to move. It is the movement that keeps the joints "oiled" and functioning...so try to do something every day.