Thanks for the thorough answers guys. We have a conventional boiler at the moment fed from water tanks, I think it's a oil Worcester boiler under a different name. The plumber didn't say anything about converting it, just said he'd install a unvented cylinder. Our underfloor will be about 30m2, all the rest of the house rads. The UFH room also joins another room with no divide and that has rads. When you say directly, do you mean as in what a combi would be doing? I guess it would run independently.
The HRC sounds nice but I don't know if I need it, the main bathroom is probably about 20m away from the cylinder.
I've read up on short cycling and dont see how that would be avoidable without a thermal store. Also seems on the expensive side to run
Im definitely not brave enough for 4 kids either.
I'm a real novice, do you mean you have a thermal store and a cylinder, or are they the same? What's the white box in your picture? I have space for a cylinder (or similar) and the boiler in my outside store) cupboard.