Didn’t see any search results for this so I hope I’m not reposting something.
Marmalade Mum, same artist who did the MGS5 horsegirl TF of Quiet has been at it again with a cowgirl TF story (and in color no less).
Synopsis: high school girl with boyish figure works with her cute but nerdy lab partner to fix her underdevelopment. Pretty obvious how this will turn out but the art and gradual TF makes it even better.
Chemistry Class.