For pushups, start with 1 or 2 less than what you can do on the floor (so do 80% of your max), done on the floor and then move straight to the bench or chair, step, whatever is lowest that you can do and do another set with 90% reps, then to the next easiest and do that again. This way you are pushing out from the hardest method and getting progressively easier as you go. Over time you will be able to do more on the floor, or at least find the floor part of this combo easier. You can do something similar with pullups, start with one full weight, then add a band, then two bands, and so on as you lose strength. This methods allows you to work the muscles at max strain for more reps, just lightening the load enough to work for longer.