Pine floor on concrete slab with underfloor heating

[Jeslia]

Hello.
I've browsed through hundreds of threads about pine floors but can't find what I'm looking for. We're planning to build a single-story villa on a concrete slab with water-based underfloor heating. We want a solid pine floor, 26*165. The supplier strongly advises against gluing it and having it floating, instead recommending that we lay an 18 mm plywood board and fasten the floor to it. Another option is to lay joists and fasten the floor to them instead. I understand that both options are not ideal from a heating perspective, but which is the least bad? Would be incredibly grateful for an answer

 

[Mr Sound]

Would follow the supplier's advice though I would have placed a plastic between the plywood and the concrete.

 

[Jeslia]

So it's plywood that is the best option, feels like there will be a lot of heat loss. It will be the same with studs since air insulates. We probably need to give this a good think.