When I was younger and leaner (lighter) and climbing a few grades higher than I do now, I used to do the plank with feet off the ground, and then do footless push ups from the plank! (With hands nearer the hip and fingers pointing away from the body).
Nowadays I can manage the no feet plank for about 8 seconds and then I collapse! Oh, the joys of just 15 years of ageing!!! I can squat LOADS more than I could then, though!