Consider looking at this
https://www.govt.nz/browse/housing-and-property/insulation-and-energy-efficiency/paying-for-home-insulation/ - the govt is offering up to 90% of the cost. A wheat bag heated in the microwave for 1-2 minutes and put on where you're feeling cold is effective and a lot safer than a hot water bottle - I spoke to someone recently who had had one burst on her lap when it was full of freshly boiled water. All the comments about curtains are appropriate - not sure if there was one about ensuring that warm air cannot enter behind the top of your curtains, drop down over the cold windows and pop out from a gap between the bottom of the curtain and the floor ... and spread across the floor to cool your feet
