Fingertip pushup also helps to strengthen your grip. Putting your thumbs and pointer fingers together in a diamond shape also increases the difficulty. Setting your legs up on the couch or raised positions makes them a tad harder. Also I personally find keeping your elbows back against your body instead of clear out changing how the pushup feels and increases difficulty. It is now weird for me to out my arms out!
To make it extra fun do your 19 pushup then go down slowly, hold until you can't hold no more then go up and call it good!