I don’t really know of a way that you can add insulation without taking up interior space, exterior space, or replacing the wall with more modern materials.
What about the sides of the home not facing the street? Can you add an exterior layer of insulation and then new exterior siding to those walls?
On the side facing the street, you could replace the stone wall with a different type of wall that was more thermally resistant. This would of course be a major undertaking.
I am sure you have considered fully insulating the floor and ceiling as best you can.
If rodents and or insects are a concern, look into Mineral Wool/Rockwool Insulation.
Many places have a long experience in dealing with cold, which my country lacks, hence I’m asking here for advice. The default solution was either endure it or burn more wood.
I may be able to shave off one or two centimeters of the total volume required as the walls are currently covered with a very thick layer of cement that was set with no concern to prior levelling the stone (in places where the mortars started to fail I chipped away to clear the loose material and there are spots where 2 to 3cm of cement could be saved just by grinding away an edge of a stone) but going by the solutions my market has available, I risk needing to layer up to 10cm of material on my walls.
I do intend to insulate floor and ceillings as they will be, for all practical purposes, rebuilt, as the current wood floors are thin.
The house is squeezed between a pedestrian street, where I can’t encroach, as there is little room already, and another house. I do have one wall I intend to insulate from the outside as it faces an empty plot.
Mineral wool I have been looking into it but I was warned it wicks moisture. Is this true?