We have completely renovated the house we bought and now we are at the stage when we have to install the plywood subfloor in the bathroom, on top of which we'll put ceramic tiles. How thick should the plywood be?

3/4 ply and then a cement board underlay. there are other options http://www.homedepot.com/p/Schluter-Ditra-323-sq-ft-3-ft-3-in-x-98-ft-5-in-x-1-8-in-Thick-Uncoupling-Membrane-DITRA30M/100199338?cm_mmc=Shopping%7cTHD%7cG%7c0%7cG-BASE-PLA-D23-Tile%7c&gclid=CNetx4b6k8oCFYElgQodX_wAzg&gclsrc=aw.ds