Thanks a lot for your help. I am already shy to ask more questions, but this part:
3. Row 1 knit. Row 2, knit first 5 stitches (for hem), perl to end. Add an eyelet every 2 inches or so on the "waist" edge to pull some cord or elastic through. Add some short-row shaping every 4" or so to the "hem" end to accomodate your hips.
I am afraid I didn't understand much how and where to add the short rows shaping (which will be a first for me, but I found the techniques's description on knitty.com)