I bought six of these from the £1 shop, they are the same metallic silver cellophane sheets that they wrap round marathon runners or people who are losing heat. Apparently they reflect infra red radiation and are good retainers of heat, so on that principle they should do well as a new ceiling liner for the yurt. Took about half an hour, but I now have what looks like a radio telescope for a ceiling. The crinkling sound will take a little getting used to, but it's no worse than being kept awake by something akin to an ostrich stomping around on the roof.
So far, the combination of additional insulation and the reflective sheet is pretty impressive, right now it's 14c outside and 18.8c inside with the only heat coming from me and the 12v fridge. I'm hoping to be able to get away with less coal and wood burning this year and lean more towards more controllable forms of heating like an oil filled radiator or fan heater.
Also, the yurt has a new veranda, I fell through the old one and nearly broke my leg. This time it's been done with decent wood from a pallet place in Wisbech run by a lovely chap from Holland who also sells timber. It's been treated with epoxy varnish so should last better than the bare wood that was used previously. To be fair, the old steps didn't do too badly, they've been there from the beginning of the build.