Big rugs, over as much floor as possible. Have fleece blankets tucked away in the living room for evenings in front of the telly (my kids have them first thing in the morning for breakfast too). A snuggly throw of some kind will make your sofa feel warmer when you sit on it.
Top up your loft insulation. It doesn't matter if you have some already, put some space blanket over the top (find it on special offer and it's dirt cheap). It makes a really big difference.
Plastic panels behind radiators are good and cheap. Check all your window frames. We found ours were poorly fitted on the outside, letting in draughts, so we used filler and sealant to close those up (and in one particularly bad one, expandable foam filler).
Everybody needs slippers or bed socks. My two are shockers for keeping them on, but it does make a difference to padding around the house.
I put up extra curtains behind my normal curtains. Curtain wire stung across the window with a thermal curtain of some kind (I actually made my own from Ikea fleece blankets, but anything will do). That plastic film that you put on windows with a hairdryer works, and is probably less noticeable than bubble wrap. If your windows are not double glazed, then you MUST do it and also tape up the edges of your windows with masking tape for the winter. In fact, if they're draughty, do it anyway. It does make a difference.
Keep bedroom doors shut to keep them warm (really works for my kids' rooms).
Obvious, but everyone needs to wear a vest. Kids and adults. My OH has thermal sleeveless vests from M&S under his clothes at all times, and I have spaghetti strap vests under my clothes. Kids have a vest mountain (all sleeveless plain white boys vests from Primark) and wear one religiously.
