After reading this thread I've realized that for me it depends what I'm doing. When I'm in my own bed, I very much prefer to be very cold, probably around 16 or 17c. But then I'm hiding under the duvet to keep warm.
During punts, I don't like to be hot, but because almost all of my punts are on top of the duvet, I tend to get colder faster than in my own bedroom, so I prefer it to be a bit warmer, maybe 19 or 20c, but no warmer than that. And of course most of my punts are in rooms without air-con so they tend to be much warmer than even 19 or 20, at least during this summer with all of the heat.