hydronic floor heating system efficiency - using concrete as thermal energy store or not?
A very important factor in deciding to use a thermal mass to store energy is the energy source. Solar energy is the classic example. The energy is free and the supply is periodic and unpredictable. Energy storage is a must.

You mentioned a boiler, so you likely are burning fuel, directly or indirectly, or at least paying for the supply. In this case, energy being of significant cost and in virtually ready supply, energy storage is not warranted. The inherent losses in the store/release cycle make it of little benefit. Especially with only 2.5cm of insulation.