Do you have to stick to another "M" name? If you can't find anything you like, I would probably just move on, and just look for a name you both love together. I like Micah (although Miles and Micah are probably too close), Matthias/Matteo, Magnus, Meyer, Moshe (or even Moses, but I like the Hebrew Moshe much more!), or even Max/Maxwell/Maxfield/Maximilian (or even something like Matthew nn Max or Mackenzie nn Max... or Magnus nn Max, works, I think.).