There should be another layer for clothes under the armor so you can add socks, trousers, shirts and headgear.

Maybe it should use ring slots so you can combine it with bring me the rings lol

I thought about using the 4 rightmost bauble slots. Do you think it would be very intrusive regarding other mods that use these slots? I mean, like, are these slots used for something besides thaumcraft's goggles of revealing? (the only item I can think of atm)

Yea it would be a bad idea I can give you a list of the mods i use (over 300 so a pretty good idea of a worstcase scenario) that would conflict with it

An alternative which is what was originally suggested could be made more easily by looking at a mod that does something similar and is open source. The betweenlands adds gems which you can add onto any armor. I'm guessing the whole adding extra data to an item of a specific type is the main issue here. So that might make it easier for you to implement something similar.

If baubles compat was the route chosen, I would recommend you make it possible for any slot just for simplicity's sake.

Is there a discord where we can talk about this so we can talk together a bit more smoothly?

Well, there wasn't until now :D. https://discord.gg/bHuzSB

Would it be possible to make an addon to baubles which would add such slots? I know Zabi made a thing which added more rings https://www.curseforge.com/minecraft/mc-mods/bring-me-the-rings
I don't know how difficult it would be to add new types of slots but I figured it may be easier using baubles as a backbone. There is also cosmetic armor which also adds different slots. Just different places you can start looking if you need inspiration lol.

@mxnmnm The Baubles approach seems kind of promising to me. I have never looked into it that much, so maybe it's the right time to do so. It seems @zabi94 actually made a coremod and used ASM to accomplish adding additional slots. But I guess using the pre-existing baubles slots is still an option. Maybe only that it may conflict with other mods, if you know what I mean.

@zabi94 Yeah we discussed it on discord, and we settled on the separate inventory approach.

I have no idea what this is, but why not just make a completely separate inventory with new slots, then add a keybinding to open it, and/or overlay a button on the inventory screen that just opens a new screen?
Maximum compatibility and control, easy to implement (seriously, don't go the bring me the rings way, it was hell to implement, it's raw asm), no need to have baubles as a dependency.

This one is going to be especially tricky. Like, I could possibly made it that you can pad your existing armor for isolation, but it would just double the amount of registered armor in the game. The (optimal) solution would be to add new slots to the player inventory, which is the tricky part. I have only seen 2 mods done this in the past: Tinker's Construct and Galacticraft.

an easier solution maybe to add compatibility with https://www.curseforge.com/minecraft/mc-mods/armor-underwear-mod/files which was originally for tough as nails (before it got discontinued.) However i am not sure if this mods is still updating or not and i am not a programmer so idk if it would work or not.

That sounds interesting. However, as you said, the mod is probably no logner being updated or actively developed. But despite that, it would be much easier and also significantly less error prone to use something already available at hand, rather than composing a whole new system. Anyways, it was meant for TAN, so I think it fits the idea nicely.

EDIT: As good as this idea was, it fell apart when I looked at that curseforge page in detail. The Armor Uderwear mod is closed source, which basically means nobody except the author can use it outside it's intended scope (which is TAN mod). Making minecraft mod closed source is outright evil, and even more when it's a library. Also, the mod is closely tied to TAN (required dependency, which basically means it would likely fail without it), so it is nearly impossible to use it.