I think the most common (and versatile as well) one for us native speakers would be:
「パッと」 is not a bad choice, either. It just sounds lighter and more conversational than 「ふと」.
EDIT: 「はっと」 is also a common one.
I am not a native speaker, but I think I have a word that will work in this case.
In English, "on that note" essentially means "let's end there," or even "well then." It is a phrase that you use to essentially close a topic of conversation, table it for later, or to create an opening to physically leave if needed.
In my Japanese experience, a lot of ...