As it happens, the 18-19 degrees is more than comfortable (even my wife who's the ultimate "chilly mortal" finds it cozy).

The underfloor heating distributes the heat all across the room, so there aren't any cold draughts and we dont get cold spots (except right up close to the windows) or red hot radiators. The room feels warm all over and the thermostats keep the temperature quite even due to the thermal inertia of the floor, unlike radiators which go hot & cold.