It’s always been Mom in the West Midlands. My mother is from Tamworth originally and although my parents moved to Norfolk when they married, this was what l called her from the time l could talk. When I started school at nearly five, l almost immediately switched from Mommy to Mummy and pumps to plimsolls, thus fitting in with the other children. I still catch myself saying Mom from time to time. I can’t see anything wrong in it. In any case, although Americans might spell it Mom, it sounds like Marm to British ears.