Wiring Question About Elect Heater

Hi again!
I would like to install a baseboard heater in my mothers bathroom. Her place is an old Victorian about 120 y.o with oil heat. The bathroom is always chilly in the am and living in PA it's the norm this time of year.
Was thinking a 27" or 36" heater between 500 to 750 watts.
My questions are, can I get waway with 12-2 on the wiring or should I go with a thicker wire? Also, should I add a GFCI breaker on the dedicated line? I'm thinking 120v unless you think 220v would be better?
Thanks!