Some wisdom that I've accumulated over the past 13 months of living here...
Get rugs for your floors.
I did this as soon as I arrived because they helped make the place feel more like home, but they also help your feet stay a bit warmer because they keep you from stepping on the cold faux-wood floors. As the ondol heating systems can get quite expensive, putting a couple rugs down can stave off turning on the heat.
For those new to Korea, my LPG heating bills ranged from 75,000 to 247,000won in November to February. The heat was set low at night and when I was out. When I was home, it got set between 16 and 20C.
Buy some mountain climbing pants
The winters here get cold—yes, while I grew up in Wisconsin, I never did care for its cold weather and biting winds. Cheorwon’s similar but it (thankfully) gets less snow.
You can find these in markets, on the street, or in stores for between 10,000 and 90,000won around October-March. Most will look like regular casual slacks, but they’ve three big differences: they resist stains, they dry sooner, and they’re warmer. Imagine wearing pajama pants until a pair of jeans or trousers and you get the idea. The quick drying helps immensely too because we don’t have driers over here. I’ve picked up 3 pairs now and I’ll be wearing them all winter here.
Get space heaters
I didn’t do this the first time around and learned my lesson for this year. I hit G-Market a month ago and picked up two 450/900watt heaters for the place. The heaters have the added bonus of drying clothes much faster than air-drying them: What once took 1.5-2 days now takes ~3 hours. I’ll put a picture up to demonstrate this later.
The electrical bill hasn’t arrived yet, so we’ll have to see how what the damage comes to later.
Get an electric blanket
I bought one by accident because I bought a blanket at E-Mart without looking too closely at the label. It’s worked well for staying warm at night or for watching movies on the laptop.