With old masonry wall construction, you need to be very careful about how you retrofit insulation to the walls. Insulating the interior makes it very likely that you’ll have moisture-related degradation of the stone and grout making up the wall, as you’re cutting off drying potential from the interior side of the wall. If it’s possible, insulating the exterior is your best option, otherwise you’ll need to be very conscious about selecting vapor-open insulation and finishes on the interior side, which will limit your options considerably. This article from Building Science Corporation goes over some of the details, and offers some options for interior-side retrofits that might not cause the wall to fail down the road.