At this time, I think the best choices for backpack Live controllers would be the Akai APC Key 25 or the APC Mini...
Having said that, I have python scripts I've been writing for Ableton Live that would work with basically any Arturia controller with buttons or pads, but I'm not quite finished yet, and it'll probably be at the end of April before I have anything that I can share with others. The scripts I have written were originally designed for the MiniLAB, but since I recently got the Beatstep, I should be able to port the scripts without too much trouble.
The way I understand it, it costs a lot of money to have Ableton custom write control surface scripts, so Arturia have stuck to providing only minimal User Remote Scripts for Live.
I spent so much time writing mine that I'm considering selling them but I'm going to at least need testers some time here in the near future...