Can anyone point me in the direction of a safe backer board to use in a polypropylene sleeve? I will be placing an autographed CD insert in a 5x7 pouch, and I was looking for a backer board to provide some support. I was hoping to lean it in the corner of a book shelf. Would it be safer to just some how attach a backer board to the exterior backside of the sleeve? I've spent the last hour or two reading on backer boards, and I'm still not confident in what to look for. Below is a link to the sleeves I'm looking at so any suggestions on sleeve brand is appreciated as well. Any help is appreciated.

http://www.archivalmethods.com/product/film-print-sleeves