Oddly enough, the older I get, the more athletic I'm becoming, but that doesn't mean I'm either slim or trim (food for thought: what's the difference between slim and trim?
I have no idea).
Anyway, from what I can tell by the reading and listening I've done (and I've done a lot!), a bike saddle is made not to cushion, but to serve as a perch for the sit bones. And while women's sit bones are generally wider-spaced than men's, whether your pants size is larger or smaller (to put it delicately) doesn't affect the size or spacing of your sit-bones--bones are bones, regardless of how much flesh surrounds them. I was told to sit on a street curb to get the feel of where the sit bones are and thus get an idea of where/how your bike saddle should support you.
That said, I've been using a Terry Liberator saddle for several years now, and on rides both short and long, the saddle simply disappears from my radar screen. And again, I don't think I'd fit anyone's definition of slim/trim.
"The road to hell is paved with works-in-progress." --Philip Roth