The nether isn’t as hot as it looks, footwear is definitely necessary to traverse it, but the fungal network cools the ground quite a bit, even within biomes such as the nether wastes. It is a warm dimension, but no hotter than the desert, with around 40° average.
Although the fungal network cools the netherack, the little to no wind and tight spaces do multiply that heat, the ground may not be hot comparatively, but if you’re squeezed between walls and a ceiling of equal temperatures then the heat does rise and may cause issues. Tighter caverns are warmer, while open, rounder caverns are cooler as the shape helps trap the small breezes.
Blackstone and basalt can be used to ward off heat if walls are thick enough, about a meter or two of either also cools whatever is inside.
Fungus heavy biomes such as the crimson forests (and subcategories) moderate the temperature even better.