Minecraft's player models always annoyed me. The slim model type barely helps at all in my opinion. So I looked for a mod that allows you to change it. Eventually I came across a mod called More Player Models which allows you to do exactly what I was looking for. And to top that off, it's available for just about every Minecraft version after 1.0. I don't think it has come out for any versions above 1.12.2 at the moment. You can find it on Curseforge. Also of course I DID NOT make the mod.
Here's the proportions I used to get this model:
You no longer have to be a T H I C C. Unless you play on a server I guess. Like honestly this looks so much better.