The enchanting loop thing is real, and honestly you're hitting on something the base game doesn't balance super well. The jump from "no enchants" to "fully enchanted" is way too steep.
Here's what I'd actually do: cap yourself at one piece of per-school cost reduction gear. Not a full set. Just one item - say, gloves with Destruction cost reduction. That keeps you functional without hitting the "spells are free" wall. Then use your other slots for stuff that doesn't trivialize things: Magicka regen, elemental damage boosts (those feel good without breaking difficulty), maybe a single piece with Magicka itself.
The real problem perk is the one in Enchanting that boosts your enchantment strength by like 25% per rank - that compounds hard with cost reduction and suddenly you're at +50% on a single item when you're only level 20. If you're trying to stay Legendary-hard, maybe just... don't level Enchanting past a certain point? Weird suggestion but it works. I've done runs where I cap it at like 40-50 and never go back.
If you're on PC, there are mods that rebalance enchanting to scale less aggressively, but I get it if you want to stick vanilla. Requiem completely reworks how enchantments work if you ever want to try a total overhaul build - cost reduction is way less powerful there, but the tradeoff is the whole game's harder anyway.
What school are you trying to use mainly? That might change the answer a bit.
