If your small board is 112L, you might as well go big with the 133L, especially if you are only planning to just use it as a light wind flat water option. I don't think there is really any advantage in going for the 122L.
www.guycribb.com/userfiles/documents/EarlyPlaning.pdf this guy cribb guide does a good job of setting out the proper gear setup and technique to get planing early. Something that I don't think is mentioned in the Guy Cribb pdf is batten tension, make sure you have this set correctly as it can have a big effect on sail efficiency.
Gear wise I think a big board/smaller sail combo is a lot easier to get planing then the smaller board/big sail. In particular you don't have to work as hard to get on the plane. What helps me the most is being light on my feet, so I pump hooked in and hang most of my weight through the harness. You need to run long lines to be able to do this AND keep the rig upright and powered up. Generally I use 2-3 back hand pumps and simultaneously hang as much weight on the rig via the harness to drive all the sail power down through the mast base. I give the board a bit of a jiggle with my feet to help pop it onto the plane.
I don't usually bother with the full body out of harness pumps unless I'm trying to stay planing on the exit of a gybe.