I think it's already been suggested, but I'd get a gaming mouse. There are some affordable ones that have a ton of buttons (the one I use has 12 on the side and a couple near the LMB and RMB). It's super handy, and you can customize the keypresses on the mouse and combine them with your keybinds in-game with alt, ctrl, and shift combos. It takes a bit of getting used to, but it's really worth it.