With no magic I assume you mean no magic items.
Dragonborn scales gift gets 13+dex+shield ac, defense fighting style, at level 10 dragonborn gets another +1.
So 14+5+2+1 = 22 AC. I'm sure there might be better options, but that's what I've had at my table.
Of course with magic he had a +1 shield, a ring and cloak of protection, that gave him a resting AC of 25. Then he'd have wizard's haste for +2, blur to impose disadvantage, and shield to make sure that the few hits that came through would miss.
Oh, and later on there's a maneuver that gives you a bonus to your AC equal to your PB- shield was still slightly better, but Expert Sidestep is only 2 exertion and exertion is basically limitless for fighters in late tier2 and beyond.
Not only that, but Heightened Reflexes means that they get all the reactions they'll need.