Insulating under first floor/above crawl space
I have a 110 year old house and the underside of the first floor is not insulated, so the only thing between my crawl space and living area is the original pine floor. First of all, how bad of a situation is this in terms of energy loss? Assuming it needs to be addressed, about 70% of the house is over a crawl space that is barely accessible. It takes a pretty small person to get in there, and it's still an army crawl to move around. I've begun digging it out from the cellar, but, aside from the amount of digging, there are gas pipes and HVAC ducts in the way. I should also note that the perimeter of the cellar (brick foundation) is not insulated and does have leaks. I feel like I've got a bad situation here, so what are my best options? I would guess that ideally, it would be dug out with modifications to the HVAC where needed; liner put down; and insulation installed. Short of that, is there anything I can do that would be second best?