What kind of fish would do well in my tank?

I have a ten gallon tank with a lighted hood, a filter, and a heater. Currently, I have two fish in the tank, a male sword tail and a high fin black skirted tetra. I want to get one more fish to add to my tank, I wanted a rainbow shark, but after some research I thought a rainbow shark might be too aggressive. Does anyone know if I could still keep a rainbow shark in a 10 gallon tank with my other 2 fish? If not, what other kinds of fish might do well?