I am fitting overlay wet underfloor heating onto an original concrete base. Its the polypipe type. The finish will be carpet & the instructions say 6mm ply on top of the pipes. There are various types of ply from super quality multiply to cheap centre heart ply (Far Eastern) & I wonder if one is better than the other for thermal conductivity or if there is a purpose made covering available. In a perfect world Ally would be the answer but its a tadge expensive for 30 m² 
