Maybe not a best solution,
Did you have a unused transformer (from Audio amplifier or anything) that have both 110/220 primary winding?
I'm sure you can make step up/down with it...(after safely insulate the secondary winding)
about the rating just make sure the transformer is rated for more then 90W (as far i remember the heater have about 70W rating)
with the configuration:
0-110V
0-220V
step up/down..