You can add a thin stabilizer to the fabric. You can certainly sew it down.
Another option is to sew a decorative stitch across the trim piece and then add in to the pillow case.
Make a flange trim piece and top stitch down the seam line. Then add in to pillow case per directions.
Add a decorative ribbon across the trim piece.
FYI: Check the pillow size against the cutting measurements to make sure your pillows fit. Some of the patterns aren't quite big enough for the fluffy pillows.