TIL that normal maps are really important for this sort of stuff. You can get away with using regular mods at smaller sizes, but once you start adding folds to things, you need custom normal maps for them to look right.
Compare my previous two posts to this one:
Note that this is NOT my work (aside from face, but that’s not the focus here), I took both the slider stuff and normal map from arca.live (can’t remember from whom because it’s in Korean, but you can find it pretty easily by searching for “bbw,” “Skyrim” in Korean and “site:arca.live”
Now if you’re trying to have weight gain mechanics rather than just a fat character, you can have normal maps for both twigs and whales with mostly seamless transition as there is a mod that switches normal maps with higher weights and you might be able to use it to make the character sweatier too. The only problem is that it works only on actual weight slider, so, if a mod merely changes specific sliders that aren’t that, it won’t work.
At the same time, real weight slider is also the only reliable means of making the face fatter with higher weight, so, you might want to switch to that anyway.
Also, for those who want to use coldsteelj’s sliders in Skyrim SE (not an option for LE yet), download Devourment Refractor from LoversLab, it has necessary files for it. It’s a vore mod, but you don’t need the rest, just Bodyslide stuff.