Riding a bike does not stress any one part of the body - your weight is spread among your arms, back, and hips.
Bicycling also has options... indoors on a stationary bike, or outdoors on a road bike.
On a recumbent bike you sit low to the ground with your legs reaching forward to the pedals. This may feel better for you than sitting upright. The seat on a recumbent bike is also wider than the seat on an upright bike.
A mountain bike has wider tires and are heavy. You can also buy a larger seat to put on your bike.
Make sure the bike you buy has a weight rating at least as high as your own weight.
