Underfloor heating-Uninsulated Slab

Really struggling with how to heat our kitchen diner 8mx6m. Most of which is on an uninsulated slab.

Does anyone have experience with retrofit underfloor heating? Is it just a little bit less economical or will it just not heat as intended.

Alternative is chasing lots of radiator pipework in plus gas fire. But I cant help feel the floor is going to be unpleasant without underfloor heating. Cost difference between the two is much of a muchness.

All advice welcome. Did trying searching but wasn't loads of info

Cheers

Josh