[fastpat]

Years ago I wanted to put that kind of tile in a kitchen. My contractor strongly recommended I do some other type of floor covering unless I was going to pour a slab to install it on. His reasoning was that, no matter what I did, the floor joists will move around when walked on, or moving appliances in and out of the room, or other things and that would mean cracked tiles and forever regrouting the floor. This was in a house built in 1917 with real 2x12 hard pine joists with bridging. Cutting the stuff was like cutting oak.

There is one thing you might do to reduce the movement, and that's replace the subflooring with cement (aka green board) and a thinner sheet of plywood, but I'm not sure that would work to stiffen it up. You could lay cement board on top of your current subflooring which would make it much stiffer, but a lot more weight which might be getting towards the limit of your structure.

We had a tile floor in CA laid down directly on particle board by the PO, and it did exactly what the contractor warned me about all those years ago.

Then, last, ceramic or quarry tiles are very unyielding, anything made of china or glass will break if dropped on it, and it's hard to be standing on for long while cooking.

It does look great, though.