I’d use a 6×2 timber frame inside the walls, shutter it and infill between the shuttering and the existing stone walls with a hemp lime mix giving you a good depth (say 200mm) of insulation, finished with a lime plaster. the timber frame can carry the upper floor joists as well so no need for any blockwork. Don’t lay a conventional concrete floor with a damp proof membrane, you will most likely cause damp in the stone walls. Use coarse stone followed by gravel for drainage then leca for insulation and a limecrete slab. The external render should be lime also. If it isn’t, remove and replace with lime.

I don’t think using modern materials in an old building is a good idea.