All TK's 359s are configured with lieflat seats, 1-2-1. A small subfleet has private cabins in J (the "turkoflots" config'd for Aeroflot but delivered to TK).
The info on TK's website reg. Aircraft type assignment is 100% correct.
That being said, info might change

TK routinley swaps planes for ops reasons. I don't think anyone can tell you with 100% certainty if your flights are going to be operated with A350s or other types.
The A350 hard product is decent. I am among those who considers the old 2-2-2 / 2-3-2 J config on TKs A333s and 77Ws to be of equal - if not better- quality as i usually travel longhaul with my wife so a 2-x-2 config doesn't bother me that much, and i do appreciate an open cabin and essentially limitless legroom.