See my post
here about my ordeal, but I have the same cover and have had it on exclusively. I survived a 6 foot fall going 55MPH+ because I had it in a daytimer cover. It is an "At-A-Glance" leather daytimer that measures 6.25" x 9" x 1" that has a zipper that completely encloses it. I removed the calendar and cut about a 1" slice out of the part the calendar slid into to allow the back cover of the light wedge cover to slide all the way in. It was about $25 dollars for the leather one, but now I think it was well worth it.
The measurements I mention are outside dimensions. If you look for anything that fits the 5.5" x 8.5" calendars, that is the size that fits inside the cover.