Meanwhile, I can feel an outside gust of cold wind from the middle of my home. I don’t begin to know where to start.
Found that out the hard way when three years ago during our first Winter here, the water to the kitchen was frozen for most of the month of January. Thankfully our house has PEX piping, so no burst pipes for us.
Sealing and insulating those areas has made a tremendous difference, even in the interior areas of the house. Since the subfloor is wide open, a cold breeze from one spot can suck the heat out of the entire floor with surprising effectiveness.
You're correct that it doesn't make sense to insulate between floors, but you do need to insulate the entire exterior wall area, which includes the wall space between floors.