This was the second pair. I tried 1 strand of yarn to understand the pattern & see how I liked it as written. I thought it it was too thin & the boot went too far up in the back - looked a little bottom heavy.
Doubled the yarn (cream & neopitan held together), use same hook size 3.75), took 1 row of fp/bphdc out before crocodile boot cuff. Used 2 strands on 1st row of crocodile stitch & 1 stand of yarn on remaining 4 rows. I also liked the boot inside out when starting the fphdc rounds so the ridge connecting the sole & boot is on the inside. I therefore had to imagine the fphdc was sometime opposite than written instructions. Minor change which was why I had to go step by step with the first slipper. The instructions were a little confusing when you had so many rows and counting but once you do it once, the next time is a snap.