Having determined the answer was one corset, I had to start making the thing.
When I was but a young costumer doing fest garb on the cheap, there was a technique we all could do mostly in our sleep (and often did): the duct tape corset pattern.
None of us had dress forms, and couldn’t have fit them in our apartments even if we could have afforded them. The solution to “how do I learn exactly how every bit of me is shaped, exactly to size, but in a form I can use to sew from” was the duct tape corset.
The idea is simple: You put on an old t-shirt and have a friend wrap you in duct tape. When your friend then (carefully!) cuts you out of it, you have an exact mold of your torso, which can be cut apart and smooshed flat to make a pattern.
The sources I used are likely long gone by now, but this one seems to work similarly to what I recall.
I now have a pattern of Shoryl’s torso, ready to be manipulated into a corset.
A Twist of Metaphor 
I still use duct tape to this day. While forms are lovely people change shape. To be truly fitted it needs to match where you are today!
Yeah, definitely! I’m not even quite the same shape I was a year ago, much less 20 years ago when I made my last corset!