The two examples of bookmarks I gave below were 2×8 — but those are too tall for mass market books. So I went for stubby (2×6) instead (these show up on my screen actual size, in case anyone was wondering).
Poor guy. I had to clip off two inches to make him fit. Also, squishing text into smaller fonts (sigh) and taking out some of the text at the back (like the names of the novellas.) All good fun.