I have a small pond - any recommendations for fish?

Very small pond - 30" wide, 6 feet long, 18 inches deep at the deepest parts but a lot of it more like 12".

Are there any small fish that stay small and will also survive our climate? (I have a little pond heater I can put in there if it looks like it will freeze)

I have 9 small goldfish (feeder fish) my friend got me from Petsmart, but doing a little research they only recommend one or two for a pond this small.

Someone here recommended rice fish, but they have only had them a few months so not sure if they can survive our heat.