Not to be rude, but the common goldfish is a bad choice. (Any goldfish, really) They produce so much ammonia, and can live more than 20 years! They also need 100+ gallons, unless you go for fancies which need 20G and then 10G for each additional one.. Please don't get a goldfish.. They need a lot of food anyway. Go to our mother site, tropicalfishkeeping.com and then search at the "Tropical Fish Profiles". There's a lot to choose over there, you might wanna look.
Over hundreds of bettas die in their small, dirty cups each day. Only you can help them live. Research and then save them, today!