Hello Kath and welcome to the forum.

I'm not a retrofit expert but I can start the discussion of with probably a lot of questions and a few suggestions.

First off, roughly where are you? And is your property exposed to winds and especially wind-driven rain or is it fairly sheltered etc? Those things can make a difference to what is suitable.

When you say 'internal walls' do you mean the walls between rooms, or the internal face of the external walls? How old is the house and is the external surface stone or something else (e.g. render)? A little bit more information about the history and the construction might be helpful. Do the suspended floors use timber joists, and are they on the ground floor or an upper floor? (How many floors are there?) Presumably the concrete floor is on the ground floor and is more recent than the house itself. Are the floors approximately level and what's the ceiling height? i.e. how much height could you lose to insulation on the top of the floor.

You say the encaustic tile floor is ruined. I'd be tempted to take up at least some of them to get an idea what is below. If some of the tiles can be brought back to a reasonable state then you might be able to sell them to offset some of the cost of your refit.

I wouldn't let the height of your first stair step dictate how you insulate. I'm sure the stairs could be adjusted if necessary.

Hi, thanks for responding, I live in Ramsbottom, bury, end stone terrace on a main road , so not isolated re: wind and rain from all sides. It’s not listed or in a conservation area.
The lime mortar is covering the the internal side of external walls.
Internal walls are brick as are chimney breasts. I have removed 2 brick chimney breasts from upstairs room in outrigger for space and intend to do same in kitchen beneath.
House was built in 1875, and has original double outrigger, random stone at the rear and dressed stone to front and gable end. No external render. House has a ground and first floor.
Slated, hip roof. Slate roof on outrigger.
All floors mentioned are ground floor, Suspended floor with timber joists is at front, facing NE. Concrete floor is in back living room and kitchen with kitchen floor being covered in Ashfelt.
Encaustic tiles in hall which runs alongside the gable, they are on dirt, I think, as when vestibule was removed you could see some dirt, it wasn’t concrete but entire hallway floor sounds solid. Tiled floor has channels cut into it by previous owner so I thought they were ruined, didn’t think about selling them so will look into that.
Ground floor ceilings are 10 ft. Internal door frames have been lowered as have lintels 1-2 bricks above current door frame/lintels .
Hall and front room floor board downstairs are same level. Back living room concrete floor and kitchen Ashfelt floors are same level but they are approx 2-3 inches higher than hallway floor, presumably as original floor (flags?) was covered with concrete at a much later time.
First floor ceiling have been lowered approx 40 cms and is now completely filled with Thermofloc and approx 400-500mm of glass wool on loft floor. This made an unbelievable difference to the upstairs temperature last winter.
Hope this is enough

Uncertain about asphalt floors, are they glassified bitumen? Asphalt would be very unusual as it dents where weight is applied

Oil based products can dissolve polystyrene which causes it to shrink back I think