there's a bunch of fic on scribblehub that might fit. a lot of them are more focused on eggs hatching than the transition itself, but there's some overlap

here's one, here's another, here's a third one

idk how you'll like them but they have happy endings and are about transbians early on (including pre-transition). they're pretty ya in vibes

also if fanfic is ok lemme know because i have way more of that