It has been a while since you posted this so maybe you've already decided, but I'll pitch in some thoughts just in case. In a French Country style, slate tile could look stunning. You could use rugs with it as well. I have radiant floor heat and tile is the best for heat transfer so the floors will be warmer in winter than you could get with hardwood.

You don't say where you live or whether you are using electric vs hydronic radiant heat, but those are other topics you'd want to think about in a sunroom application. Eectric is usually local to the room so you can have quicker response to temp changes, whereas hydronic is slower and usually the main system for the home. If you live in an area where the outside temperature changes quickly from cool to warm or vice versa, you would want to consider that.