Retrofit underfloor heating?

Hello,

we would like to retrofit underfloor heating in the lower living area. So far, radiators are installed.

Which system would you recommend?
I have heard of a thin-bed underfloor heating system that is connected to the existing heating circuit. Do the radiators have to remain for this, or can the supply line be connected directly to the underfloor heating?

Best regards

I once saw something like this on the Rotex homepage. They mill into the screed and then lay the pipes in it.