Marissa is wrong and Bizz is right. No fish can live happily in a bowl. Especially not a goldfish. The common goldfish get to 12 inches and are incredibly demanding fish. Keeping a fish in a bowl is like you living in your high school locker. Bettas need at least 2.5 gallons of heated water. They do not really need filters if you keep the tank clean, but since they are tropical a heater is really important. Here's a quick solution so that you can keep fish happily. Buy at least a 3 gallon container. (Some fish bowls are that big, some aren't) Get a whisper 1-3 gallon filter for like $7.00 at walmart to keep your tank clean. Then, either buy a heater of no more than 10 watts or: If your room stays above 75 degrees F at all times then you can just buy a cover or make one out of tinfoil (make sure that there are holes for air) to keep the tank warm. Also, buy a thermometer for like $2.00 and stick it on the outside of your container. If your tank water drops below 75 degrees the you should buy a heater.
Note: Heaters can melt plastic, so if you have a plastic tank beware!
Good Luck!!