There are plenty of ways to increase difficulty, such as NPC Enhanced (I believe is the one I'm thinking of) which gives NPCs better AI, healing potions, etc. One among many, many difficulty increasing mods.
Yep, and I think I have them all.
NPC Enhanced, MCA, Unleveled Creatures, Greater Undead, The Undead, Morrowind Advanced, Creature Pack 1.1, Creatures, and GCD setting hard.
At level 37 using only an amulet and two rings - none holding a constant effect - and armour with only the cuirass enchanted with 10% constant shield, my Redguard can smash his way through them all as long as he's careful. Two handfulls of rings would I believe make him immortal.