Since I was using a heavier yarn, I cast on 18 sts on US 10/6mm needles, based on another pattern. But I did the squares in the “L” pattern and folded them following this pattern.

I only knit 17 ridges per square instead of 18, since that seemed square.

The slippers still came out a bit too big for my 8.5 to 9-ish feet. I had to send them through 4 full wash cycles to get them small enough. If I knit them again, I would only knit 16 sts.

I’d also probably modify the squares to make a less-pointy heel, like in this project.

They ended up fine, but I still prefer the Duffers slippers.