I wish I could tell you but our 1960s thermostat not only has wild up to 5°c temperature swings but does it's own thing once we go to bed And just sweats us out at 27-28 (even though I set it around 20) until I turn it down to 18 at which point it goes down to 15 or below. I'd prefer 18-20 while I sleep. But apparently that's not an option in our house.
And SET at 26c? I'm sorry, but you're the responsible adult in that relationship. He can put on a t-shirt and pants.
Yes, because murder is illegal. But if they never find the guy... That's okay too.