you should really check out the Figura minecraft mod (https://www.curseforge.com/minecraft/mc-mods/figura), it allows you to use fully custom avatars, and anyone else using the mod can see your avatar, it’s available on most versions above 1.16.5 and on most modloaders

if you don’t want to make your own there is a discord server that does have some available for download

if you do want to make your own though you can use Blockbench which is a free modeling software for minecraft models, it also uses lua for scripting, which you can use to add custom functionality to your avatar

(imma also include this, its a free api for adding ear/tail physics among a bunch of other things https://github.com/MrSirSquishy/SquishyAPI in case anyone needs something for that)