We are gutting to 2x10 floor joists. Baths are approx. 76x120. 1969 home. Common wall between 2 upstairs baths. I have 12x12 porcelain 1/2" tiles. Leaks through common wall (not plumbing). 1 wall sunk near common wall. What subfloor would you recommend? I have heard mud job, 2 3/4 ply with mesh above it, 3/4 ply with durrock or hardibacker. Also not sure what type of thinset (home depot has Flexbond).

Thanks for any advice.