I’ve been using a Korg microKONTROL with my MM. It’s compact, has both USB and standard MIDI I/O, optional battery power, and has a joystick and pads. I think its size, functions, and brushed aluminum face and endcaps make it a good pairing for the MM and/or MD.
Here is a shot of it with my CZ-101, for size reference (sorry for the wonky barrel distortion):