Floor tiling question

Going to tile the floor of two adjoining rooms making them into onw, having made an opening. One has a concrete sub floor, the other has wooden floor boards.
The concrete floor is about 20mm lower than the wooden floor.
Rooms are each about 15 square meters.
As the rooms are rather large we thought of using Wedi or Marmox Boards. 10mm on the wood and 30mm on the concrete.
Is the right way forward, or should we just screw plywod on the wood and levelling on the concrete?
Any one out there used Wedi or Marmox Boards? Any good.
Cheers JohnO
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