Have you looked at how you current pillowcases are constructed? They used to be carefully constructed with three pieces of fabric a body, cuff and small trim accent with medium cotton weight. Today they are often one piece of fabric with a fold at the cuff, and a single stitch, no trim, no decorative detail. Maybe this is due to overseas manufacturing or just a lack of attention to detail. To lower prices, the materials used in bedding is increasing lower quality lighter weight cotton. Sometime Microfiber, which is polyester, polyamide and/or polypropylene, or pretty much plastic, is offered. It just falls apart, pulls, and doesn't drape well at all.
100% cotton doesn't always mean quality, soft fabric. There are different weights of cotton (it doesn't matter what country it came from). For our pillowcases, we use a medium or quilt weight cotton that is also measure by the ounces per yard, ours is 3.3oz PSY. This is a thicker, stronger textile and will lay better than the commonly used light weight cottons such as percale or broadcloth. We find these cotton weaves are too light weight for pillowcases resulting in a look that is loose, sloppy and generally doesnt drape well.
The medium weight cotton can handle three time the "double rub" of a lightweight cotton. Double rub is a use test to measure abrasion resistance, thus a machine rubs fabric thousands of times to measure when it breaks down.