So far, exercise is the only thing that reduces my anxiety. I need it to balance me out. When I don't exercise for a while I get extreme anxiety. Personally, I run, but I know you have bad knees so walking, bike, hiking or swiming would be good ones. Swimming is great for you, you work everthing. Oh, you and your husband can do a home palates or yoga.
I also think the stretching advice is good. Stretching for anyone is a healthy choice. Good luck.