You can make a screed floor as thick as you want. Ideal is about
10-12" from teh soil, with hardcore, sansd blinding, screed, Damp
proof membrane, insulation, then pipes-in-screed. Or wires I guess.

Unfortunately, I don't fancy installing a concrete floor to a kitchen that
has already been fitted. Such a solution may well be regarded as somewhat
disruptive.

Christian.