I would like for there to be a way that I could have the appearance of a costume without the benefits so I can one have one uniform outfit bonus and mismatch sets to customize my appearance.

So only one outfit bonus is available even though I may look like I'm wearing multiple different outfits.

My Suggestion is the "Outfit/Costume Journal"

Instead of breaking down an outfit for Crones/ Valks you'd have a third option to add it to your Costume Journal.

When you equip another outfit you could have it look like the outfit you just equipped or an outfit saved in your Costume Journal. (You cannot remove outfit/costumes once placed in the Costume Journal out this would be permanent, and class locked.) 

Only the outfit/costume actually being worn would have the benefits effect the character if the Costume Journal item was chosen it is purely cosmetic with no game altering effects.)