Completely agree Di
Welcome Macaroni
You are best to get the biggest tank you can afford and accommodate
If you haven't got the room for a big enough tank for goldfish, other coldwater fish you could have that stay small are minnows. There are a few others that are classed as tropical fish but some people keep them in cooler setups.
Personally I prefer tropical fish and think they are easier to look after
Whatever you chose, all fish need a filter in the tank. And that filter has to be matured by cycling the tank before adding any fish
Think about what you can accommodate tank wise and we'll advise you with what you will need etc