Most any of the live bearers will work and won't get too big for the tank:
Guppies, Swords, Mollies, Platies, Mosquito Fish, etc. can handle temps into the 60's and are fairly tolerant of temp fluctuations.
Danios will generally work as well, but they can be aggressive toward other fish, and depending on species will outgrow the tank.
Tetras (which Silver Dollars are a family member of) generally need to be above 72°-ish and some, like Cardinals, even in the low to mid 80's.