Another slider I've thought of is a hip width slider. It'd be good for making thicc legs not clip into each other.
If you want some inspiration for sliders I'd recommend Street Fighter 6's, which apparently has some the most comprehensive slider sets I've yet seen.
Another good one is Fallout 4's character creator with the mod "Extended Facial Sculpting - Now With 90 Percent Less Beta" installed. To my knowledge, there's not a character creator out there with with options for such minute detail modification. Here's a link: "https://www.nexusmods.com/fallout4/mods/25087", no videos I'm afraid.
Perhaps you'll find some good ideas to implement from these examples.