About halfway through game and aven't beaten it before, is there a no-turning-back point to NG+ that I should watch out for?

I'm working on the Lord of Hollows ending and I'm in Irithyll. I don't know anything about the ending of the game other than the steps involved in obtaining this ending.

I want to do as much exploration and any optional areas as I can in the late-game, but I don't know when that is, and I'm afraid I'll beat a boss and suddenly a cutscene will play and then I'll be in NG+. What should I hold off on doing if I don't want to trigger an inescapable endgame?