I've used polystyrene boxes (you can get them from fishmongers, some butchers) and stood some of the small plants in there as extra insultation for the winter. A couple of layers of fleece on top provides a cosy home.

Also saved any polystyrene packing sheets from parcels and lined the shelves of the metal staging.

I find it helps to move plants as high up as possible, to get lots of light and get them away from the coldest part of the house. Whole house gets bubble wrapped (it's only small).

For the coldest nights, using a small paraffin heater - although it seems to be getting harder to find places that sell paraffin, garden centres seem to charge a lot for it.