I would highly recommend cycling. I do a daily circuit of the local country lanes with fairly hilly sections of about 7 miles - takes about 40-45 minutes. The great thing about the bike is the lack of impact stress (and the downhill sections!) Having been recently very unwell, I have needed to lose weight, so in just over 2 months with a combination of exercise and diet I have lost 7kgs. This I find unbelievable, since I have been trying to lose weight for years - but illness and a loss of one's medical tends to be a hell of a motivator!
Good luck - I am living (thank God!) proof that it can be done.