goldfish get sick at the temps bettas need. and, they're VERY messy fish. the one i had as a kid was ALWAYS pooping. x: one fancy goldfish needs 20 gallons to itself. they're social fish, though, and do better with another goldfish, and each extra goldfish needs an added 10 gallons, so for two, you'd need a 30 gallon tank. common goldfish need MUCH bigger tanks, and really do best in ponds. Koi should NEVER be kept in bowls. they get HUGE and are messier than goldfish, i've heard. they're pond-only in my book.
never keep a goldfish in a bowl. you'll condemn it to a short, horrid life. you can't provide ANY of it's needs in a bowl. they need filtration, and room to grow. they can live 20+ years if taken care of properly, and the common goldy i had as a kid lived 13 of that with a pleco(the weird sucker fish you spoke of). he would have lived longer, if my dad hadn't had the habit of tossing whatever small fish he caught while fishing, into my tank. :/