Goldfish companions

Question
I have a 32 gallon aquarium with at the moment very young goldfish and would like to know if there are other fish that could be housed with my goldies.  I have no heater, could a heater be put in with them as some people have stated to expanded my options?  I have never put a heater in with goldfish and I am very hesitant to do so unless an expert says will work and not harm my fish. Any help you can give me would be greatly appreciated.

Answer
Is it a fancy goldfish or a comet/common goldfish? If it is a fancy goldfish it'll have a round tennis ball body and swim in a waddling manner whereas comet/common goldfish are long and torpedo shaped with longer fins.

If its a comet/common you definitely shouldn't house anything with it until you get a 75 gallon or larger with double/triple filtration.

If its a fancy goldfish it is perfectly stocked and you could house a 6-8x school of White Cloud Minnows or Danio's (who can withstand same temps). Goldfish are really coldwater fish so you could create lethargy if you added a heater.

Then I wouldn't recommend adding anything else.