I want to use mouse button 4 + numbers for certain spells but doesnt seem to work

Is there an addon or such i can use?

yes there is if I am understanding what your asking correctly. there is a whole list of open keybinds you can add your extra mouse buttons to. left and right click cannot be bound to more than one however even using shift+click. I will look and see where I cound them and add another reply shortly
ok might not be the best answer but heres how I did it
go into key bindings , action bar. theres a whole list of the action bars and the keys bound.
bind the keys you want to action bar areas. I even added shift+click to my extra keys to double the bindings.
I use the default ui not sure how this would work with an add on ui.
hope this helps

This post was edited by Cynr on Feb 13 2017 02:47pm

Im pretty sure only mice with software features such as the razer naga have the option to make a certain mousebutton to act like a modifier (shift, alt ctrl)

cheap 5 button Logitech didn't have any issues but good point.