Display of trims on custom armor and elytra on chestplate

I made a datapack which let's you combine the netherite chestplate with the elytra. Now I want to make a resource pack to show the elytra on the armor as an item (which already works) but also when worn. 
I added the "wings" layer to the netherite file of the equipment but that makes the Elytra always visable but I only want it to show when they are combined. And when I apply any trim to the armor the elytra changes to the "no texture"-texture and the armor doesn't change visually as an item.
How can I make that work? Is it even possible the way I want it to work?