Monks do not need defensive options. Monks have plenty of defensive items to choose from with the tailoring update and can hit some of the highest numbers in AC aside from a Pale Master Death Slaad.
If you truly wish to give monks something to spice them up but not add to their existing power, it would be to expand on monk weapons. Quarterstaff. Kama. Nunchuku. Shuriken. These things all have one guiding factor: monk weapons pale in comparison to monk damage die scaling on their fists.
This goes not only for just monks though. Any ambidexterity build or two weapon fighting build is not pleasant to play in the itemization meta that exists in PotM. Finesse weapons all enchant poorly and give poor amount of damage bonuses when crafted. Right now, here are the meta options: 1d12 and 1d10 strength weapons. Bastard sword and tower shield. Greatsword/Greataxe/Heavy Flail with improved parry.
This is because those weapons have a much stronger damage die from the crafting bonus and the enchanting bonus. The crafting bonus on those larger damage die weapons (1d10+) still makes the crafting bonus useful even with any sort of enhancement bonus. For smaller weapons like Kukri, Kama, or Shortswords, however, that crafting bonus is just overwritten. For any elemental metal like Darksteel, that bonus is only 1 of an elemental type for those smaller weapons which even enchanted ends up poor.
You have to address the underlying issue with the crafting system and that is that smaller, finesse-based classes are on the bottom of strength based weapons that end up stacking an absurd amount of damage on top of already high base damage (strength 1.5x, 1d8-1d6 crafting bonus, 1d8-1d6 positive energy bonus). That isn't even taking into consideration the feat tax that comes with two-weapon fighting.
To swing this back around to monks, you can't give monks offensive variety because they only have access to the types of weapons that have smaller damage die.
Enchanted Steel Kama/Cutting Wheel/Nunchuku/Ect.: 1d6 damage type, +2 slashing bonus, +2 enhancement, +2 positive damage
Enchanted Darksteel Kama/Cutting Wheel/Nunchuku/Ect.: 1d6 damage type, +1 electrical bonus, +2 enhancement, +2 positive damage
Compound that with monks having 3/4 AB, the -2 from flurry of blows, -2 from two weapon fighting (with all the feats). For damage finesse classes pour dozens of feats into their build for a minimal reward of maybe 0-2 strength bonus, 3 if they're lucky. How does one this compete with 1d20 fists that have no malus outside of flurry of blows? Not only can monk weapons simply can't compete in their current state, but no finesse weapon can compete against a martial that only has to put improved parry and martial proficiency in their build for more damage, more AB, and similar AC.
My suggestion:
All finesse based crafting weapons need a revamp, given additional AB enchanted and extra positive damage. Does this affect other classes than monk? Yes, but expanding options does inadvertently grant monk OTHER options.
A suggested permutation:
Enchanted Steel Kama: 1d6 slashing, 2 piercing, 1d8 positive, 3 enhancement (4 with addy)
Enchanted Darksteel Kama: 1d6 slashing, 4 electrical, 1d8 positive, 3 enhancement