After ordering Steel Boning from Corsetmaking.com, (which was, ironically, cheaper than the plastic boning that I originally bought from Joann's Fabric hoping to save some money) I am, at last, happy with the look and fit of my Stays. No more buckling and creasing. The difference is like night and day, and they feel like a second skin.
Before Back: (and here's where it makes a BIG difference)
If I was pleased with my stays before, I am ecstatic now! Steel boning is a miracle, and I will NEVER (repeat: NEVER) buy plastic boning again. Lesson learned.