I did Couch to 5k a couple of years ago. (I've been thinking of motivating myself to do it again, because I foolishly let it slide.)
The advantage is that you can do it in your own time and take as long as you want over each step. The audio which goes with it is, in my opinion, a bit annoying but it does keep you going. The programme gives you waystages, but it doesn't matter if you take longer over each one.
It starts off very gently with a mix of walking and jogging and builds on that.
I have problems with my feet and have to wear socks and trainers with lots of support, so it's mildly painful for me to walk anywhere, but somehow having a goal made me forget about the pain. I also wore a heart rate monitor while I was exercising.
It would be a good idea to talk to a doctor or nurse before you start (if you can get an appointment). If you're really out of shape just start off going for a timed walk a few days a week - maybe half an hour and increase your distance as you feel comfortable.
Rather than spending money on a programme, you could search the NHS for exercise programmes. From memory, there are a number, including chair exercises and programmes for older people.
Good luck! It certainly did me some good.