I'm not a grandparent yet. However, I do work in maternity. Many women are called; Nana, Nanny, Nona (Italian), Mima, Babi (short for Babusha or Babushka -Ukrainian or Russian), Mimi, G-Ma, Gram, Gammy, Gramma ____ (followed by given name Gramma Sarah), Grammy and Mawmaw.
I've heard slightly less variation for the new grandfathers; Papa, Poppy, Nono (Italian), Grandpa, G-pa, Didi (short for Diduece - Ukrainian), and Pawpaw.
Good luck. Sometimes it comes down to what the child can pronounce! Congrats in advance!