You don't NEED a fancy controller with the BK-7m. It has a mode where a simple 'one MIDI channel' keyboard gets the full layout options from the module. Basically, you set your module up in close where you can get to it, get an FC-7 foot controller for access to plenty of stuff you either want hands free or the front panel doesn't have, a sustain pedal and a volume/expression pedal (if you use them) and you should be good to go...

Something with assignable sliders for Part volume control might be nice, but if you are more of the 'set it and forget it' type, you can get away without that.