Even fancy species of goldfish, which stay a bit smaller than other types, will get as big around as a softball plus fins or bigger. A ten gallon tank simply will not work for goldfish long-term.
In an unheated tank, there really aren't many options for you as most fish species available are tropical and would require a heater in the tank. The white clouds already mentioned are nice fish. The Vietnamese variety are particularly stunning. If you got a heater, we would be able to recommend a lot more fish to you.
Since you cannot keep goldfish in your tank long-term, I would suggest returning them as soon as you can. Next you'll want to do a fishless aquarium cycle (which may well already be underway due to the goldfish being in the tank). There are plenty of guides available on this forum (for example, here
). A good liquid test kit is really your best friend when cycling a tank as it will tell you how far along the cycle is and ultimately, when it is complete.
Once that's done, it's really just a matter of knowing your other water parameters (pH, hardness and temperature) and we can give you all kinds of ideas for fish!