More weird pathfinder stuff? Sure, why not.
A great form of often overlooked defense is incorporeality.
https://aonprd.com/UMR.aspx?ItemName=Incorporeal
>take half damage from any corporeal source
>if a corporeal spell targeting you doesn't do damage, you have a 50% chance to ignore it completely
>you are fully immune to nonmagical damage (enemies need at least a +1 enhancement bonus weapon or have their natural attacks count as magic)
>if you must roll to hit, you can ignore your enemies ac bonuses from natural armor, armor, and shields,
>you get your charisma bonus to ac as a deflection bonus (this stacks with most other cha to ac things)
>use dex instead of str for melee attacks
>no falling damage
>no swim checks
>can't set off most traps due to not weighing anything
Oddly enough, classic spells like Gaseous Form DONT grant you full incorporeality. You need something like Dust form (1round/cl) or Shadow Body (1 minute/cl). The best spell however seems to be Shadow Projection:
https://www.aonprd.com/SpellDisplay.aspx?ItemName=Shadow%20Projection
>duration: 1 hour/level (D)
>gain full incorporeality
>also gain the str damage touch attack of a shadow
The only downsides are that your shadow form gets treated as an undead (vulnerable to turn undead and channeled energy) and that you need to keep your body someplace safe. Honestly a great tradeoff for a 4th level spell.
Now that's all well and good, but maybe for some reason your fighter wants to be spooky too. Assuming he's too feat starved for something like the Share Spells teamwork feat, he can still join in for the low cost of deleting his strength score.
Behold, one of the dumbest things to come from Paizo since Sacred Geometry: Ghost Syrup
https://www.aonprd.com/Necrotoxins.aspx
For the low price of 6k gold (assuming you have a way to reduce your fort save) you can gain
PERMANENT incorporeality. You lose your strength score, so don't try this if you aren't some kind of dex to damage build.
The only real drawback of being incorporeal permanently this way is...well... none of your equipment or items will be incorporeal. You might be able to walk through doors, but you aren't picking up your handy haversack anytime soon. Thankfully, Paizo was kind enough to publish the Amulet of Grasping Souls
https://aonprd.com/MagicWondrousDisplay.aspx?FinalName=Amulet%20of%20Grasping%20Souls
>Lets incorporeal creatures pick up and use corporeal items
Problem solved for 21k. Grab craft wondrous to get the full combo for 13.5k gold.
For a full caster with the eschew materials feat, you should have enough money to craft your own Ghost Syrup at level 3-4, right around when you'd unlock the craft wondrous feat. You'd be amazed at how many enemies won't have an answer for complete nonmagical damage immunity. Ignore every trap and locked door. Solo an entire dungeon with acid splash. Save the day 1d3 acid damage at a time.