Hrm. That looks like it would be tricky to make a ‘stand-alone’ pad. You might have better luck if you actually upholster them. You could glue the padding (foam in this case, I’d think) to the top of the stool, and then stretch the fabric over that, stapling it to the underside of the top. Here’s a picture of an upholstered saddle stool. If you decide to go that route, and need more tips on how to do it, let me know. Good luck!