Lolita Coats -- Staying WARM in winter?

I live in the Northern edge of the Midwestern US; as a result, winter is a huge thing. It not only lasts an unholy amount of time (it isn't common to see frost in September, and snow lasted in some areas until July a few years ago), but it gets cold out here! -40 Fahrenheit with windchill, at times, even (obviously, that's an extreme case, but an "average" winter day can easily get to -15). As a result, warm coats are pretty much a necessity.

I've been wondering where I could get a winter coat that could withstand the colder temperatures of where I live. Obviously, safety is going to be my priority, and if it's simply too cold, I'm going to be dressing for it--wanting to wear a skirt is going to be a flimsy excuse at the doctor's office when you have to explain frost-bitten legs. I'm aware of layering techniques like wool tights, bloomers (I own several pairs, and I've recently purchased some flannel to make a few winter pairs), but there still has to be something up top that can go over it all.

What stores make the warmest coats, that could stand up to this kind of bone-chilling weather? I'd prefer offbrand, as brand sizes don't exactly work for me; custom sizing as an option, even at an additional cost, would be perfect for me since I'm a "plus size" Lolita. Taobao brands, indie brands, etc--all are welcome, really. My style is generally Gothic, often with a twist of classic, so sweet brands wouldn't exactly work for my wardrobe.

If there aren't any brands that you can think of that have coats that could suit my needs, do you know where I could go to comission a coat from? If I had to design a coat myself, I definitely could.

Looking forward to hearing your answers~!