Oh… as an FYI… the tops of mine were lose. I suggest the following modifications

1. knit the pattern as is, but knit the top/cuff with an elastic strand
2. knit the pattern as is, but knit the top/cuff with smaller needles (like US 0)
3. knit the pattern with thicker yarn and knit the top/cuff with smaller needles (like US 0)
4. avoid all non-elastic yarns (like bamboo, silk, or cotton)
5. knit the pattern as is, but knit the top/cuff with a lot fewer stitches (depending on how you tight you like them)
6. knit them as thigh highs and wear garters under your skirt ;) you naughty hogwarts student you LOL