When I picture my characters while writing, they're usually anywhere between a size 8 and size 14. I personally am between a size 6 and 12, depending on the cut and brand I'm buying, where I'm buying from, and occasionally, what colour I'm buying (if you can believe that!).
I don't really think about my characters' body types unless it's key to the story. For example, if fatness or thinness is a factor in the challenges or privileges my character experiences. I realise that my choice in this matter is itself a privilege, as many women and men have to consciously and actively consider their bodies when making even the smallest of decisions.
I like to think beauty is in the eye of the beholder. If I'm in a situation where I have to describe body type, I generally aim for either functional (respective of the job they're doing) or subjective (described the way the character observing them might view them).
As a teenager, I longed for a world where body shape wasn't sensationalised or politicised. Where aesthetics were one thing, but we could generally just be ourselves, have our preferences, respect the preferences of others, and let that be that. Save for within safe spaces shared with trusted people, it's not really the world we live in yet. But with more diverse representation and shifts in perspective in books and other media, I certainly think we'll get there someday.