Based on the number of stitches around (117 I think) and the look of the stitches themselves, I'm thinking it's a light worsted weight yarn. You might do a test swatch and see how many sts per inch you get with the yarn you have in mind and see how it would work out. I think it would be more like the wash cloth yarn than crochet thread. It looks like it shouldn't be hard to adjust the number of sts to fit your gauge...unless I'm reading the pattern wrong and there is a more complicated stitch pattern that I'm missing.
This is the last time I'm frogging this project for the last time.