You can get help with insulation and, I think, heating equipment, even if you are in a rented flat.
Here is a link to an Age UK Factsheet that has a section on funding for heating improvements www.ageuk.org.uk/globalassets/age-uk/documents/factsheets/fs67_home_improvements_and_repairs_fcs.pdf .
It might be worth talking to your local branch as they will know whether any extra help is avaiable locally. I assume you are on the modern equivalent of the Economy 7 that charges a lower rate for charging storage heaters overnight.
What decade were your grandparents born?
Desperately sad story of the assisted suicide of a grieving mother



