I use KDE at work and rarely touch the mouse to switch between windows. I have two monitors, and a couple of keyboard shortcuts, but power-usage comes with a price. I bet i3 needs a little tinkering too.
IIRC, the only real tinkering I did was to re-jig the navigation shortcuts to resemble VIM bindings. From a user's perspective i3 is comparable to xmonad, but configuration wise it's an order of magnitude simpler.
i3 does, however, come at a price. Not being inside a fully functional DE means a lot of normally trivial tasks require active thought and engagement, at least at first, since they will have to either be handled via the command line or by seeking out the correct application (e.g. managing wi-fi connections, handling dual-monitors & monitor rotation, etc.)
