We have the bubble foil sheets slotted behind our radiators.
Slippers, cardis, wearing layers.
Blankets on the arms of every sofa and end of every bed.
Make use of curtains, letting in sunlight to warm things up and then closing at dusk to keep heat in.
We have a thermostat which keeps the house above a certain low temp all the time.
When you have used the oven, if it's safe to, leave the door open as it cools to get the benefit of the heat.
Hot drinks. Insulated cups so your drink doesn't go cold. Use a flask to store hot water if you are worried about boiling the kettle all through the day.
Simple hot meals. Tins of soup and beans etc to have ready instead of a cold sandwhich when you are not cooking a full proper meal.
Move around to warm up. I get so cold when I sit still at my desk for too long.
Dry washing outside even when it's cold. Get as much moisture out of the house as possible. Drying outside in Winter does take a bit longer but as long as the weather allows get the clothes on the line.
Rugs. The ground floor of our Edwardian house is freezing. No insulation under the floorboards, just the air gap and then the ground. Rugs and mats really help and have others have said, slippers and anything that keeps you off the ground.
Check the insulation in your loft. Is it still in good condition and could more be added?
All this is quite grim and I would also make sure that you take care of your mood. Daily walks in the sunshine when possible, candles to make it cosy. Eat well, sleep well. All that stuff.