You can actually use a webwork of regular wood beams anchored to stone walls to support stone floors, though the technique for getting it to work right can be a bit tricky. The laying down of stone floors like that requires that each new piece of stone floor be touching stone on at least two sides (so you need to start at a corner and work around in a collapsing spiral, like a spiderweb, or in rows, one at a time). Also, the maximum number of slabs width you can build before absolutely needing to boost up with stone pillar or wood-iron pieces obviously decreases the higher you get due to reduced stability.