I finally got it done, you can make Felix go from a somewhat skinny guy into an absolute chonker with a single slider! Customizable Player Models is required to use this btw. I'd personally recommend using this with the "overstuffed" mod, which adds weight gain to minecraft using custom player models.

You can download it here!
https://drive.google.com/file/d/1Hf.....ew?usp=sharing

Customizable Player Models
https://www.curseforge.com/minecraf.....-player-models