The other thing is - keep your curtains drawn to keep the heat in. And make sure your curtains are heavy, fully lined ones, especially in winter.
Doors closed through the house, draught excluders where needed.
Fleecy blankets whilst sitting on the sofa.
Fleecy pyjamas and fleecy dressing gowns.
Reflectors behind radiators.
Fluffy socks. Poundland ones are particularly warm.
Fluffy slippers - the boot style ones.
Don't bother to heat the hallway, and only turn on the one in the bathroom for a short time before your baths.
I only heat bedrooms for an hour or two in the evenings. We all have fleece blankets under our duvets.
Swap to a 13 tog or above duvet in winter, and use lots of layers of blankets on a baby too young for a proper duvet. Woollen first, then fleece on top.
Put tights under trousers on babies and toddlers - even boys - it just looks like socks under trousers, and it's a warm extra layer for their legs.