Personally I think a mouse is not replaceable by anything else that even gives remotely the same productivity. What can be improved is how often you have to reach for your mouse and how much your hands have to move on the keyboard.

I have personally switched to a tiling window manager that allows me to do much with the keyboard, added the surfingkeys plugin to chrome to allow the same when browsing and switched to using the neo2 keyboard layout (this is for Germans, Dvorak or something similar might be better for you).

The combination of these factors has massively improved how much I need to reach for the mouse throughout the day.