How to set up macros/keybinds?

I was wondering if there was a way to set up a macro on my mouse. I have a mouse with the 2 buttons on the side to go forward and backward. I was wondering if there was a way to make it so when I hit one of those, it activates the 9 key. I need this because I play minecraft and I want to be able to switch to the 9th slot on my hot bar just by pressing one of the 2 buttons.