Long story short I want to get a daily push up routine in addition to my gym schedule and being perfectly honest I don't see myself having the strength to do a regular push up for a long time if ever. The issue is that I'm just quite tall and at a 25 BMI while I'm not particularly "fat" I am heavy in absolute terms and I just dont realistically see my upper body getting strong enough to support that weight without a level of training that I doubt I have the capacity to do.

So that leaves me with doing push ups where I support my lower body with my knees. The issue I'm finding is that my knees are also not that great at supporting my weight (even if I didn't have a bad knee I'm sure it'd be pretty normal for them to hurt in this situation) and my pillow isn't stable enough to get a good push up without changing my position slightly with each push up which isn't great for multiple reps.

Are there any good solutions you can think of where I wouldn't have to buy anything to put under my knees? Household goods or other methods? I know I can buy an exersize mat but I don't really use them for other workouts and I want to cut down on the amount of money I spend