At the risk of sounding like a total nerd, I have used leftover padded handlebar tape to create a makeshift thumbrest for my mouse. I have a Logitech G Pro Wireless and the side buttons are super sensitive. The thumbrest was just enough friction to prevent my thumb from accidentally bumping the side buttons. I've since switched to custom-fit Lizard Skins for my mouse, but its interesting that they make handlebar tape too.