Level Based Defense Bonus in Old School?

A question for reader base.

If I was using Swords and Wizardry or Labyrinth Lord as the basis but I wanted to reduce magic items quite a bit, how much if any general bonus should I gave to AC at higher levels?

It seems to me that AC should go up a bit with combat skill and not just with magic gear so that a 10th level fighter is a bit harder to hit than a 1st level one.

My options to accomplish this seem to be some variations of....

Cyclopedia/Dark Dungeons Weapon Mastery

A slight modification of "Armor for All" at Retro-Roleplaying

Some kind of "parry rule" where I can take away from my chance to hit to take away from yours, possibly at a ratio ala Rolemaster or 3x's Combat Expertise feat . This would work better with raising AC but thats not an issue for me.

A flat class based bonus or maybe something else .....

What say you all?