Im having some problems with thinking of what to make my wing harness out of and how to do it. The wings will be made of foam board and are pretty large in wing span, however they will be quite light weight.

It needs to go under a thin costume like a school outfit/shirt/blazer so i cant have it too bulky either.

Can anyone help me?

The harness types I can think of are PVC, a backpack, and a strap harness.

PVC probably won't do because of the uniform, and it might be too bulky unless you get small tubes. If the wings are quite lightweight then a strap harness or backpack will be useful, a backpack might be a nice touch especially if it's a school uniform

Can't help you much with finding tutorials though, but hopefully a google search of backpack wing harness or strap harness might help. Good luck!