Do you currently have a regular bicycle? If so, consider picking up
one of these. I bought one a few years back and have put enough miles on it since to require a new rear tire. Its quiet and smooth and you can easily change the load by just shifting gears.
I shattered a knee at Cannon about thirty years ago and biking was the key factor to restoring my active life. The knee is fairly arthritic now and frequently hurts a bit, but hopping on the bike for few minutes is all it takes to make the pain go away, motion is the lotion. By the way, I still usually get 35+ days at Cannon each winter ...thanks to biking!