My Mum was Nanna.( my Dad was first Gangar, then later on, his first name. Both decided by my son, and copied by my daughter).
My paternal grandparents were Granny and Granddad.
MrLP and I would have liked to be Grandpa and Nanna, but sadly we have no grandchildren, and it's not looking likely. I think those of you with grandchildren are so,so lucky.
I went through a stage at work, (when everyone seemed to be having grandchildren, there was a new announcement nearly every month), when I got so jealous I could hardly speak. I did work hard to overcome it, gave my congratulations, bought cards and knitted for the new arrivals, and admired the photos. It's easier now I'm not working!
So OP, choose whatever name you feel happy with, and enjoy your new role. Congratulations!
Take care xx