I have a couple yoga mats, and took the older one and cut it into a mat for my TKL keyboards. It works great and silences the one of my KBs by eliminating the key-strike sound from bouncing off my computer tabletop. It's not noticeable with my MX Red keyboard because so much sound comes from the surface of the exposed KB; but on my 55-gram Realforce, it does absorb sound that resonates from the keyboard's base and bounces off my tabletop. This has been an inexpensive, moderately silencing addition for my 87UB. It wasn't noisy, but not it's even quieter than it had been.
The yoga mat I used measures 3/16" thick. The are sold in different thicknesses: 1/8", 3/16", 1/4", and 3/8". I'm sure a 1/8" mat would have worked fine.