Hello,yes, I can offer advice on underfloor heating in your existing solid floor kitchen.
I built my house ten years ago without a heating system so my kitchen is under heated too. It is warm enough due the very high levels of insulation and the no draughts at all methodology employed during construction.
My first points of advice are to ensure that you have done all the necessary draught proofing and air sealing, next is to upgrade insulation. Both of these two actions will reduce the heat loss from your kitchen, possibly sufficiently so that you don’t need to increase the heat input.
Floor insulation is rare but in my view essential with underfloor heating as the floor becomes the warmest place and in some cases more heat (which you pay for) escapes downwards than upwards where you want it. I would like to see several hundred millimetres of insulation underneath underfloor heating pipes, there are thin systems available but generally the screed thickness recommended is between 65 and 75mm, plus any reasonable amount of insulation means digging up the floor and starting with it again. The only viable time to economically do this just before refitting the kitchen, it could be done by refitting the existing one, either way it will be hugely disruptive.
The cheaper option would be to draughtproof and insulate and then add more heat input via larger or additional radiators providing the boiler can cope. If space is an issue then fan convectors may work for you or plinth heaters.