most monster evolution stories just make the mc a human with claws or something after a few chapters and 90% its a busty woman as well.

Chrysalis stays a monster and a no bewbs for at least the first 100 chapters (as far as I've read).  https://www.royalroad.com/fiction/22518/chrysalis

Check out my story, A World of Monsters. The MC remains a monster, in the true sense of the word. 

Mine is the other way around: MC starts out as human and becomes more and more monster the further the story goes.
The first change is in chapter 6 if you want to give it a try. Children of Nemeah Book 1 | Royal Road

I post one chapter per day until the first book is finished 

The Snake Report
Stays a snake, goes down magic path rather than giant monster snake path

The Great Cores Paradox
Snake will almost certainly stay a snake (is an ouroboros)

The Stained Tower

The MC is something akin to lich, dryad, soul reaper. Her being is split in three. Her body is anchored to a place and grows into forms like living glass. Her spirit is mobile but is something akin to a leaky ghost made of disease and madness-inducing haze, her soul is the violet flame within a stained glass heart at the core of her being. She lacks a mouth and thus cannot speak. She constantly bleeds away essence and thus must feed in order to maintain her existence.