No unfortunately :(
Mage armor and shield spells
Silken ceremonials are useful if you REALLY wand that +1 AC at no cost.
Still, be careful it's not too heavy for you and then makes you fall in medium encumbrance.
Why would NOT wearing armor give you an AC bonus?
Well, realistically, wearing armor makes you easier to hit, but harder to injure. It isn't hard to understand why the game's AC system might confuse newer players.
The AC in this game is an abstraction, and can be quite a counterintuitive one at that. When someone doesn't hit your AC, there is no explanation for why/how they missed. Maybe their attack wa good, but your speed and reflexes were better. Maybe their attack was a wild swing. Or maybe they hit with monstrous momentum, but the magic of your armor absorbed the force of the blow.
How they do or don't hit is purely narrative, and there isn't any direct way to correlate the AC system into the narrative of how the attack missed. So, there is a bit of a disconnect there. Why does the guy in full plate tend to dodge attacks more than when he isn't in full plate? Most narratives I've witnessed in my gaming experience tend to mix it up, the how of the miss that is.
The result is that any random guy tends towards being able to better dodge while in full plate than while not in full plate. Odd? Very.
Anywho... It is easy to see why someone who might be a little new to the game might see the way AC works and get a little confused... and then maybe come to the rules forum and ask some questions.
And, generally speaking... when someone is asking questions or seeking help... the sort of response you’ve given is less than desirable, and certainly unhelpful.
As for actually answering your question directly, I’ll say this: Most classes with lighter or no armor proficiency have alternative methods for ramping up their defensive capabilities in some way instead of armor. For a wizard, their method is spell use. But, not all classes work this way, some actually derive defensive benefits while not wearing armor, or wearing lighter armors. The game has an internal balance for this sort of thing. While heavily armored characters do tend to have higher AC, or higher potential AC… the other characters generally aren’t much farther down in AC potential. They almost universally have an alternate route to ramp up their AC.
How they do or don't hit is purely narrative, and there isn't any direct way to correlate the AC system into the narrative of how the attack missed.
Actually, there's a very easy way to correlate this!
If the attack misses, but the roll was still better than the touch AC of the target, then you describe it being deflected by their armor or shield. If the attack was worse than their touch AC, then you describe them dodging the attack. If the roll was a natural 1 or the total result was 9 or lower then you describe a wildly inaccurate attack.
Totally agree that the AC abstraction can be confusing to beginners.