single best recommendation for you is walking.

walking in fresh air is very healthy, and I encourage you to do this - if at all possible. But i understand that you said ... there is a limitation.

Next best thing is an in-home treadmill. I suggest that you get one that can incline up to angles of 10-degrees, and preferably 12-15 degrees. That way you can easily adjust the "rate of exercise" from ...easy workout ... to real calorie burner. It is WORTH spending the money to get a good-quality machine delivered and installed to your home. One extra nice thing - you can watch TV or movies while walking.

Other machines, including "elliptical machines" and stair climbers ... are also effective. But if you are over 60, the basic treadmill is the best, I think.