Hello! I would say that an even better way to write is is "I have only been there once" because it is actually the adverb telling us more about "been" so it makes sense to have it before the verb. I hope that helps!

Definitely "only once" would be more idiomatic in almost every situation -- but I could imagine something like "Why do you keep going there?" and then, in a firm voice: "I have been there ONCE ONLY." Or "I am going to say this once only, so listen carefully." It would be only for emphasis, though.

I have been there only once.

I have been there only once. Or, I've been there only one time.

"Only once"