I have seen time-laps videos on Youtube of a company that retrofits houses that have crawl spaces with full basements. It is pretty amazing to watch them work. They hand dig out sections at a time and pour footings and supporting walls, they then do a final pouring of the floor. They do this without lifting the house.
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.