FYI on most off-the-rack corsets- they are made for people with very little waist curve. This means that if you are pretty curvy (or want to be)- you will need to alter it.
This can be done! Easily!!!
Here is how:
The corsets are sold by waist size- 24, 26, 28, etc.
You are better off buying the corset to fit your HIP size and taking it in at the waist. One of their underbust corsets will have a hip size of about 4-6 inches bigger than the waist size. Take your hip measurement over whatever skirts/pants/etc you will wear the corset over. Yes, this is bigger than your actual hips. Then subtract 6 inches. Order that corset size. Once the corset arrives take a dart in the side waist panel on each side to reduce the corset waist size (not the top and bottom) to the finished corset waist size you want (about 4 inches smaller than your natural waist.
My example: For my last OTR corset order, I bought a size 42 waist corset, which had a 47″ hip measurement. I then took in the waist only to reduce the waist size to 34″. Had I ordered a size 34, the hips would have only been about 40″ and way too small over my hips with skirts on. (38-34-40 approx.) By being willing to sew a couple of darts, I ended up with a nicely curved corset with measurements of 44-34-47!
Want one that fits right to all your curves right out of the box? Try Mystic City corsets, and have a measuring tape handy.