I agree. Installing tile direct to a wooden subfloor, (has to be double layer), can work, but is not recommended by any pro that knows his/her business. It should never be done where dampness can occur, such as a bathroom. I also recommend either a tile backer or Ditra. Ditra is my first choice, use it if you may get it in the amount you need?
TILE GUY - retired- TROY, MI - Method & Product suitability consulting.