It depends what follows the preposition. If you are talking about travelling (i.e. "been" is past participle of "to go"), then "to" is correct: e.g. I have never been (travelled) to Ukraine. If you are talking about position (i.e. been is past participle of "to be"), then "in" might be a good choice of preposition e.g. I have never been in trouble / in hospital. There may be some ambiguous situations like prison. It's usual to say : "I have never been to prison", which means "I have never been imprisoned". But if you wanted to clarify that you had never been inside a prison building, you should use "in" or "inside".

If you're "going" to a place then you use the word "to". Examples: I'm walking TO a park. Have you ever been TO Disneyland. I'm running to catch the bus. If you're inside a place or a object then it's in. Examples: I'm IN the car. He's in the store. The kid is in the stroller.

'I've been in' means that you visited some place and came back to your country. 'I've been to' means that you visited some place, but you're still there.

If there is travel involved, then you use "to". We use this preposition to mean transit. "I've never been to Boston in the fall." In comparison, "in" is static.

You can say "in" if what you are referring to is something you can be "in." "I have been to the beach, but I have never been in the ocean."