My friend used this pattern from Indygo Junction
http://www.indygojunction.com/patter...rids_grommets/
and just added another layer inside with a zipper down one of the side seams. The piece just goes to the bottom, which she reinforced. Very unnoticable to the unknowing, and even others that "tote" were surprised that it was so concealed.She loved it with a few caveats. Her handles did not hold up, the thick cording came apart multiple times at the joins, so she replaced them with just a flat stitched strap. Also, after some use, one of the grommets came away from the fabric (probably from the weight of her "piece") so her next one would just attach sturdy straps and skip the grommets altogether (they are sorta pricey anyway!)
She has this pattern, waiting to make it, the side pockets are Very roomy!
http://www.studiokatdesigns.com/quattro.htm
She suggested
www.wholesalepatterns.com as another site to look for your needs.