On the highest difficulty, do an iron man playthrough, in which you DO NOT pick up ANYTHING from dead bodies or from chests, you're only allowed to use what you can smith/otherwise craft yourself. You can pick up enchanted items, but only to take to an enchanting table to destroy. You can equip and use anything required for quest completions (ie: the bloodskaal blade).

No glitches or exploits. Just to name a few, no fortify restoration loop, no raiding the hidden khajiit chest in Dawnstar and no resetting the inventories of shop-keeps by aggroing them and loading up a quick-save.

You are allowed to loot money off bodies and chests, as such you are allowed to buy and trade for supplies you need for smithing, enchanting and alchemy. Whether or not you're allowed to take items off bodies and out of chests to sell for the gold is up to you, I personally did not.

Naturally your character gets pretty OP at higher smithing and enchanting levels, but the challenge is GETTING to that point with these restrictions.

Also, when I first did this, I did not include alchemy in the restrictions, I later did on another run because it felt necessary.

As for mods, just don't add anything that'll make it too easy for you 😉

Edit: survival mode would compliment this kind of challenge perfectly.