The one suggestion we hadn't taken was to leave a window a little open - with minus 7 degree temperatures outside I was really reluctant to do that. With him downstairs, we opened the window of the nursery and shut the door, and within 2 minutes the temperature had dropped from 18 to 12 degrees. I left the window on the latch then, and let the room warm back up to 16 degrees. It seemed to do the trick though, as when I eventually took him back to his cool but full-of-fresh-air room, he dropped straight off and slept until 7.30am.
The upshot is that we don't have any energy left, after the 4 hours of screaming. I can't imagine doing anything energetic, so sat on the floor this morning and wrote J-cub's thank you cards for all his lovely Christmas presents. We took photos of him with each of his Christmas presents, then got cards made up by Truprint. They are lovely, you can put 3 photos on the inside as well as one on the front. They were expensive, but with all our recent illnesses I knew that if I was to handmake them, the recipients probably wouldn't get them for another month.
Now they're all done, and ready to nip round to the postbox when either of us can muster the energy to get dressed.