"Multiboxing" 2 characters - advice appreciated

I am farming Naxx 25 trash mobs for a transmog item. My DK tanks and self-heals while my Balance druid does some DPS. I have two monitors that I switch between in order to press buttons for each character.

The issue, naturally, is that switching between the two monitors manually like this is very ineffective - my druid is geared to do maybe 6k DPS but is doing on average 3-3.5k DPS. I must also concentrate 100% all the time so as not to mess up my DK rotations with self healing and keeping diseases up, all while trying to dps with my druid.

This might sound stupid, but does anyone have advice on how to improve the "flow" of the process without using a multiboxing program?

Or is a multiboxing program the only solution?