These slippers are knit holding two strands of yarn together. You could use one bulky yarn instead, be sure to check the gauge. These are knit in the round to minimize seaming. The bind off shown is kitchener stitch which can be intimidating but it’s worth it to hide the toe seam. Here’s a great video with instructions on kitchener bind off.
http://www.youtube.com/watch?v=I7jIzwO5Nv4