Paradise fish

I got this fish tank but idk what can fit in it. I don't want any fish that needs a heater or anything I want a cold water fish or like room temperature. It just this tank is small, idk what to like get I live in Shrewsbury and I always go to Maidenhead aquatics, any help? It has already gravel on the ground, and a wallpaper at the back, so but the filter needs to be on so the water is cycled right? First I was thinking about a paradise fish, or like. A weather loach but they get too long and no swimming places so I can't. I just want to be happy with maybe like fish that are like, you know friendly and will come to you and stuff. See less