Natural stone MUST not have a floor tht deflects or it will crack. You need to know the size of yor joists, their length, and how far apart they are. That will tell you how much deflection that your sufloor has. At a minimum, you will probably need to install additional plywood and Kerdi to decouple the tile from the subfloor. At the worst, you would need to open up the floor, and sister the joists and install blocking and a thicker subfloor then underlayment and tile.

Look up Michael Burns book on tile; I think I've seen it at Home Depot. It's published by Taunton Press.

Thank you!

Incidentally, that's "Ditra,,," not "Kerdi."

Never install any tile or stone directly on a single layer wood floor. Adhere to the TCA guidelines. Many tile installation problems are a result of cutting corners.

I used Schluter Ditra under quartzite/slate tile flooring in my house and under slate tile in my brother's house. Neither of us has had a single problem. (My home was built in the 1970s and his in the 1950s.) Ditra instructions specify what kind of subflooring must go under the Ditra based on the width of your floor joist spacing and the size of your tile. It was quite easy to install and came highly recommended both from the forums here (mostly the Bathrooms forum) and my local tile store.