N4 — outside your level filter
Is said whole, with nothing composed onto it and takes no だ／です, so there are no forms to conjugate.
そうそう
sousouoh, that's rightN4expression
Example sentences2
そうそう、その話を聞きたかったんです。
sousou, sono hanashi o kikitakatta n desu.
Oh right, that's the story I wanted to hear. neutral
そうそう、それ、それが言いたかったんだよ。
sousou, sore, sore ga iitakatta n da yo.
That's it, that's exactly what I wanted to say. casual