I don't think anyone's mentioned it yet but legwarmers are brilliant. I wear them in bed at night (you can tuck the leg of your PJs into them if the trousers are too short) and in the day too. They're good for covering up gaps between leggings & socks.
Baby leg warmers are good for babies & toddlers to wear under trousers. They make good wrist warmers for adults too, and can be put on LO's arms at night to keep them warmer when in a sleeping bag.
Shop-bought baby leg warmers are really expensive, but I bought lots of pairs of adult over-the-knee socks from Poundland and cut them down to size - works a treat for my DS.
Knee-high socks are good too.
Our loft bedroom was 13 degrees this morning although it felt like about 3 degrees.
I made a 'tent' of our duvet and changed DS's nappy, put on his eczema cream & got him dressed underneath it. That'll save me a few pennies this year - normally I'd put the fan heater on to take the chill off the bathroom and do it in there.
Put your underwear / thermals / DC's clothes for the next day in your bed to warm up. You could do it briefly in the morning just to take the worst of the chill off, or put them in there the night before so they're properly warm when you come to put them on. :)
It occurred to me that rather than running the hot water for DS's wet wipes in the morning, it would be better to put some hot water in a small flask the night before - more efficient to boil a kettle than start the boiler up.
Split crotch fleece trousers are great for potty training / recently potty trained children - they can go on the potty without having to take off their trousers. If necessary you can pop a nappy over the top.
I'm going to experiment with putting an Ikea fleece blanket on top of the mattress, under the sheet to warm us up in bed.
If you don't use radiators for clothes drying, ceiling airers work much better than floor-standing ones.
When you have a hot drink, hold onto your mug till it cools down - it'll warm your fingers up.
If you accidentally boil a bit more water than you need, pour the dregs into a flask & pour into the kettle next time you need some water.
Try keeping a jugful of tap water on the worksurface for use for hot drinks - it'll take less energy to heat from room temperature than from the cold temperature outdoors. Keeping a lid on it will prevent condensation.
Keeping toilet lids closed and emptying sinks / baths as soon as you've finished with them will reduce dampness.
Anyone know how to produce drinks hot enough to warm up a toddler without there being any danger of them scalding themself?