Reusable hand warmers - click the metal thing inside them and it will heat up immediately - Primark and Amazon
Snuggie or slanket- Primark and Amazon
Fan heater - put it in for 10 mins - b&m they have reduced theirs to £6
Fleece bedding - use your bedding as a blanket on the sofa so will be nice and warm when you go to bed - Primark\Aldi/amazon
Draft stoppers for the doors - Amazon / Primark
Open the curtains on sunny days and closed on non sunny days
Layer up - fleece leggings and fluffy socks - Primark
Excessive while sitting down - free
Under desk cycles - exercise and keep warm anywhere from £20 and up
Soak feet in a bowl of warm water
Make sure all windows are sealed and if not use old material from clothes if you have to to block any gaps
Put blanket on you and put the hairdryer quickly for a few seconds for instant warmth
Invite loads of people over for body heat or get a lap dog .... joke