The answer is - walking. Normal speed but include 10sec burst of speed walking. In a week or two you will be able to speed walking 20 and 30 sec intervals.
Then you can try to jog - it is very similar to walking, but there is an interval when your both legs are of the ground. It is not easy switch from sedimentary life style to active moving but it's worth it. I know what I am talking about - I did this switch when I got 55yo