Inspired by this.

I used 6 strands of worsted weight yarn and a giant blue hook. Instead of working rows back and forth to create an opening, I made a cylinder, finishing the opening by decreasing until a cat-sized opening remained.

I basically made it like a hat with decreases starting a few rounds before the end.

Jim loves it! It stays collapsed most of the time because he likes to use it as a bed (just like everything else I crochet).