Have you thought about seeing if there is a local sheltered housing scheme where there may be some residents who would love to get out and about for a walk but feel the same way as you and dont want to do it on their own? Often they can be isolated and would relish some company and possibly some exercise? Even half an hour a week could be invaluable for some people - it could be the only contact they get!
Being moved along by someone who "wants your place".