Oopsadaisy1
If you don’t want major construction work (that you probably won’t get your money back on, but would make you warmer) .
Then it’s
Double or triple glazing.
Fraught proofing external doors
Thick underlay and then carpet on floors
Heavy curtains will help
I would think that heavy wallpaper has got to help on the walls,
Don’t touch ceilings as you have loft insulation.
Leave heating on low 24 hours a day and boost when necessary.
No steps are ‘cheap’ but they will make your life more comfortable.
And of course wear layers of warm clothing and keep moving about, go out each day to warm places, garden centres are good to wander around in and get a cheap cup of tea. Or just a brisk walk.
These suggestions strike me as the best you have been offered so far, and mine are certainly not better.
I just want to add a word of caution: make quite sure before installing double or triple glazing, that at least one window in each room can still easily be opened for the five or ten minutes necessary to air the room properly every day.
Insulation is a good thing, but like all good things it has drawbacks, and one might well be more condensation indoors.
Likewise laying underlays and thick carpets down is fine as long as there is no rising damp.
In your place, I would ask a builder's advice, or that of the DIY store as to what is best in this kind of building. I have no idea what it is you are actually living in as dot and dab means nothing to me.
I don't think thicker wallpaper will make the slightest difference, but as I don't know what your walls are made of, I may well be wrong.
Yes, you want to stop heat escaping, but you also do need to prevent cold air getting in!
If double glazing is beyond your means, plexiglass or even thick polythene of the type used for damp-proofing between plasterboard and rockwool, can provide a less efficient, but cheaper form or double "glazing". Both plexiglass and polythene works best fitted to battens that have the right dimension for the inside of your window-frames and can be held in place by little swivel clips for window screens.