MosquitoBait, my sewing area is also in the basement and in the midwest so can relate to being cold in the winter time. It's 2 basic rooms with only 1 having the baseboard heat in it and it's on the far side of the space. When I know I'll be doing some actual sewing/quilting and it's downright frigid, I'll plug in my space heater that looks like a radiator as I can adjust the heat on it. It seems to do the trick for me plus I keep a fleece lightweight jacket down there when I need just a little bit of warmth.
As for sashings, I like using mini striped fabrics so I keep an abundance of that on hand. If I don't have what I need, I might make my own by using 2 of the colors I want cutting them fairly thin, sewing the strips together as either light/dark/light or dark/light/dark. There's so many ways to make your own sashings by how you cut them either on the straight or more tedious, on the slant, depending on how wide you want the sashing to end up as.