ok thanks for the answer and the link.
After some research I assume that some TUI flights from Amsterdam are operated by Thomson UK, who also operate the Dreamliner. The seatmap is almost the same. Is this correct?
I am wondering because TUIfly Netherlands only has 3 Dreamliner. Thats not enough to cover all their routes.
My biggest fear is that TUIfly is downgauging the flight to a Boeing 767-300ER.