This mod adds 1 unique horse harness with 70 armor, but uses the Battanian harness model, as shown in screenshots. If you are comfortable with editing a line in Notepad, you can also change it to be any harness model you want (instructions at the bottom.)

* Manual Installation:

Drop the EnbarrHarness folder inside your common\Mount & Blade II Bannerlord\Modules
Make sure it's checked as active in the launcher.

This is a simple mod that does not replace any existing horse harness in the game (it will not be found on NPC's or available elsewhere). It is a unique ID and must be added via an editor such as EditLord or Saddled Edge.
(Go to the Inventory tab, Horse Harnesses dropdown, and look for 'Enbarr Harness'. Add 1 to your inventory.)

I mostly made this for my own enjoyment, but decided to share. I currently don't have intentions of doing any other harnesses, however this is very easy to do.

* Customizing:

If you would like to customize the mesh to look like a different harness (but still want the high armor value) or even to change the name of your harness item, simply edit the spitems.xml in this mod's folder. Rightclick and Edit, or Open With Notepad.

If you want to find all the harness mesh names to possibly use, look at the default spitems.xml found in
steamapps\common\Mount & Blade II Bannerlord\Modules\SandBoxCore\ModuleData
And search for "harness". Don't edit anything there, but you can use it to find the ID name of the harness mesh you want to use.
You should see entries such as:
        id="desert_cloth_harness"
        name="{=2Q0m5CG0}Desert Cloth Harness"
        mesh="horse_harness_aserai_a_clotest"

You should see something similar in this mod's spitems.xml, which you can change like so:

1. Changing the ID to anything unique means it won't replace a current harness in the game.
2. Copy the entire name line from whatever harness you want the appearance of, keep the {} blurb, but you may change the text name to whatever strikes your fancy.
3. The Mesh line is what model the harness uses, you could paste that in if you wanted to make the Enbarr Harness look like a Desert Cloth harness instead of the current Battanian.
4. You can also change the body_armor value if you wish.
5. Just hit Save, don't mess with the extensions, make sure it's still .xml and not .txt

* Versions:

I have only tested this on main, not beta, but as long as TaleWorlds doesn't change the code for how items are handled, this should remain functional. It doesn't mess with anything other than creating one new item, should be safe and conflict-free.