Here is a bad drawing of the tuffest pushup there is: I call it the super pushup. It works the whole front side, including muscles you didn’t know you had. It works the stabilizer muscles between the chest and abs, popularly called the “core”.
Use a pair of stools to put your feet on. Or, you can put your feet on a swiss ball. And, that could be easier to do barefoot. A pair of cheap basketballs can be used to put your hands on. The entire move is unstable, and this instability creates enormous amount of work for your chest, abs, and core, delivering maximum benefits in minimum time. Start with your feet and then mount onto your hands, and get started. Start with a few, and work up.
To go to the next level, put a small training sandbag at your side. Kneel down with the balls in place. Put the sandbag on your back between your shoulder blades. Do the pushups.
To progress up to the super pushup, first do pushups with either your hands on basketballs and your feet on the floor or your feet on a swiss ball and your hands on the floor. Progress up to what I call the super pushup, which is hands on basketballs, and feet on 8" stools. From there try mounting up for ultra pushups with the feet on a swiss ball.
Ideas for using super pushups in your workouts include using them as warmups, or the following workouts: 100 ultra pushups for time ///
5 rounds, for time: 10 ultra pushups / 10 sandbag thrusters (medium bag) / 10 pullups /// 5 rounds, for time: Run 400m / 10 ultra pushups
You get the idea. Adjust rounds and reps as needed. There are many more sandbag training exercises here.