IMO a betta could not be Kept in a pond with other goldfish. The goldfish would get extemely big compared to the betta and they would grow much faster than the betta.
Betta are beautiful fish. I currently have 2 male bettas and a female betta in seperate housing.
You could get a 5 or 10 gallon tank and decorate it up and have one male betta in it..the betta would love it! It's nice to see them swimming around. Most of the time you only see male bettas in a way too small jar just lying there on the bottom and not moving around. Once you get them into bigger spaces it's amazing to see how lively they really are.