Use butted spokes, they are certainly not weaker than straight gauge spokes.
skinny does not equal weak. unequal tension on spokes equals weak. I would have a competent LBS replace the spoke, then detension and retension/rebuild the wheel up to spec. make sure it gets stress-relieved...
also, 3X is stronger, and easier to build well, generally speaking.
and it is important to note where the spoke broke....
my 2c