The best floor coverings for use with under floor heating are hard surfaces such as stone and ceramic tile as they have the least resistance and transfer heat effectively. As the most thermally conductive of all floor coverings, energy from the heating pipe array can transfer quickly to the surface of the stone/tile. Increasing the thickness will have little effect on power output, but will slightly increase heat-up times.
It is always advisable to use a de-coupling membrane and flexible adhesive with solid floor finishes reducing the potential for hairline expansion cracks; large areas will also benefit from expansion joints, especially through doorways. The flooring supplier will be able to offer advice on specific coverings.