My personal use, I use 1/2 inch cement board under my tile. There is a 1/4 inch backer board available. Have used it under tile. I was told not to put tile on wood, because wood moves too much with temp and moisture.
I put thin set under backer board or cement board and screw it down.
I don't like using large tile over wood sub floors, it will usually pop up or crack the tile.
Wood will flex when a heavy person walks on it, so I wouldn't go larger than 6x6.
To deal with elevation difference get you a piece of oak and make a transition piece. Done that many times. A few times I make the oak piece to match the elevation of the tile and grout to the oak. Or mill the oak to go over the tile.