Whatever you do in terms of heat in a conservatory, you have to recognise that it disappears through the translucent roof really quickly. This means that you want a cost-efficient system so that the heat put in there cost relatively little. This rules out electric heaters unless there is absolutely no alternative. Conventional radiators run off the CH is the best bet for you, IMHO. UFH works off either electric mat or water-filled tubes that are embedded in the underfloor screed. The latter system is NOT a simple case of running the domestic CH water into the underfloor pipes - the temperature of the water is too high (at about 65 degrees C - it needs to be about 50). You would need a heating engineer to design you a simple control system involving a mixer valve. It is also absolutely critical that you can separately control the conservatory heating system from the rest of the house - because you will find that you only want to run it when you are planning to go in there.
Lastly if you are thinking about UFH, the sub-floor must have AT LEAST 100mm thick of Celotex insulation underneath the slab that has the pipes embedded in it. Otherwise much of your precious heat will be wasted downwards into the ground.
Given all these dire warnings, you will understand why I think you are best off extending the CH and using conventional radiators.
I have such an UFH system in the conservatory, with 140mm of insulation. The rest of the conservatory is built to Building Regulations standards (insulation in the dwarf-walls, the best glass and polycarbonate for insulation I could get), existing patio doors left in place. I run it at weekends only during the months November to March. The floor temperature (of about 28 degrees) is lovely and toasty on the feet. It nevertheless cost me about £150 per year in heat just for this one room. So do not expect that one can run a conservatory for 365 days a year in the UK - not at any reasonable cost.