Re construction - not all timber frame construction is equal. Many modern Scottish houses, for example, are timber frame surrounded by rendered blockwork (retains heat well), with good insulation inside the blockwork and sometime external insulated cladding as well. And also very well insulated roofs, and double or even triple window glazing, too.
It's very hard to judge from the photos, but the walls of the house in OP's link look rather 'thin' in comparison with several Scottish houses that I've seen. What is inside the outer brick covering? Is there a cavity? Or blockwork? And what about insulation? The roof looks 'thin' also. Is that well-insulated?
What are the roof-trusses resting on? This link shows the 'normal' design of a timber roof: https://www.designingbuildings.co.uk/wiki/Timber_roof But from the photos, you can't see what's going on behind the pasterboard.
Without a loft in that big sitting room, you'll need thick insulation. (And the heat will tend to rise up to the top of the space, so at ground floor level that room might be hard to keep comfortably cosy. ) There's also a lot of glass - what is that like? You'd need well-made, well-glazed windows to stop heat escaping. And lots of big curtains.
As I said, I can't possibly judge from the photos. The construction might be fine. But I'd strongly suggest a survey to have a proper look at the solidity of the construction and at the level of insulation/potential heat loss.