You should be fine to install central heating, although you may well need to have the pipes running over the walls rather than chased into them. I can't see anywhere obvious to put your boiler, but no doubt there's a useful space somewhere. Ours is under the stairs.
It will be cold and somewhat damp, though, I suspect, given that its set into the slope like that. On the other hand, if you run your central heating throughout the year, you can keep it at a nice temperature and see off the damp. (But this is expensive, obviously.)
You can also install secondary glazing, and that will tackle some of the draughts.
However, for central heating, is it on mains gas? Or would you be needing to put an oil tank somewhere? That does look like it would be awkward, with the lack of space. You might also want to check out past threads where people have moaned about the costs of buying heating oil.
On the question of costs, you might also want to think about maintenance, when the thatch was last re-done, approximate costs for re-thatching (£10,000 every 20 years, someone told me?).
I say this on every thread, but if you want to buy it, buy the SPAB Homeowners Book and read it first, and then if you do buy it, go on the SPAB Homeowners' Weekend Course. This will save your sanity when all goes horribly wrong.