I gave my answer before as yoga being a great exercise for your entire body. It is the one thing that helps with flexibility and balance as you get older. But the best form of exercise if the one that you will commit to.
There are many forms of exercise that you can do without joining a gym such as riding a bike even if it is a stationary bike. Walking outside, on a treadmill, or marching in place at a pace you can keep, but also working up to your target heart rate to achieve your cardio goal.
As you get older I believe it is important to have an exercise routine in place that includes cardio, strength training, and flexibility. My neighbor attends a gym class that meets twice a week for older people (she is 77) and after 6 weeks developed sciatica. Her doctor injected her hip and leg with cortisone and now she has problems walking up and downstairs. Her doctor said that she needed to build strength in her quads and so she performed exercises that concentrated on this one area perhaps a bit too much. I urged her to go to an orthopedist to get his opinion before continuing with her exercise routine. He told her what I thought, she had a muscle imbalance. She is now going to PT and it has helped her tremendously and so now she understands what it means to exercise correctly. I have been down this same path so I understand.
So while I would like to recommend a specific dvd to help you, exercise is tricky in that people will stop when they injure themselves because they either overdo things or do not do it properly. If a gym is not an option, perhaps a personal trainer who will create a personalized program for you that you can do at home. They will teach you to perform exercises correctly and you can go from there. I learned proper form from taking classes in a PT office many years ago and have taken yoga and pilates classes so that I am confident in doing these exercises in the comfort of my own home.
