Try to keep your house air dry , honest .
Wet damp humid air takes more energy to warm it up. Damp duvets and wet window sills in the morning mean alot of moisture .
I know the weather is rubbish for drying clothes but leaving clothes over a radiator makes the rad inefficient and puts the water from your clothes into the air, where it condenses onto cold suraces like windows ( think beer can taken out of the fridge in the summer )
Try to open a window, if safe ,after showering or using an airer to dry clothes , let the moist air out during the day , then shut windows when you get home from work .
Look out for 15 Tog duvets not as expensive as a hefty electric bill
Cellotape used to do tempory double glazing you taped to a window then used a hairdrier to shrink it and it became almost invisable. Good for stopping draughts, but you do need to be able to dry the air still/ let moisture out.
Stews and soups are warming . Aldi or Lidl do Crane outdoor wear and there base layers are polypropelyne . They are toasty warm and cheap.
I have a microwavable bean filled seal that comes to be with me . He warms my neck whilst my body heat fills the duvet.
Memory foam mattresses are definatly warmer than normal ones, Ikea do toppers which will insulate you in bed .
Lined curtains and curtains over open stairwells are a great way of reducing the volume of air that needs heating.
Sorry you cant afford to heat your home . Being cold is horrible . we grew up in cold 1800's house and regulaly had ice on the inside of the windows on winter mornings . DM used to heat our clothes in front of a gas fire and we used to rush to get dressed in the mornings .