Severe knee pain when sitting down and getting up since becoming sedentary. should i add height to chair bottom?

Yes: Getting out of a low chair can be stressful on the knees and a higher seat should make it less stressful. Another simple way to lessen knee pain after prolonged sitting is to bend and straighten your knees periodically while seated to prevent them from getting stiff.

You knees - gelling: We call this gelling when you sit a while and your joints get stiff like gello after setting. This can be related to knee joint arthritis, or knee bursitis or tendonitis. We do have lift chairs to help people awith knee and hip pain get out of a chair and adding height can help. Getting off the toilet can be a problem and there are raised toilet seats but you need an evaluation, x-rays.