2 item ideas for tanks and fighter survivability.

The item has an active that when activated makes the user grounded, reduces movespeed by 40%, but makes the user take 50% reduced damage from champions for X seconds. Special interactions for certain tank abilities like nautilus Q wont move nautilus but will pull the target. The slow goes through slow immunity(olaf R, Yi R, Morgana E).

That item would be intended for front line tanks and/or bruisers.

Other item would be to rework Thornmail to no longer reflect damage an enemy deals to you plus based on your bonus armor. Instead it would be an item that reflects damage back from autos based on your bonus armor that reflects back damage in a slightly different way.

Example being if you have 100 bonus armor enemies attacking you reflect back up to 150 damage but cannot reflect more than their auto damage before resistances. So a Vayne critting for 500 damage will take 150 damage while a Malzahar autoing for 70 before resistances takes 70 damage.