How to get thin layered hair?

So I just got my haircut, and it just above my collar bone. It is layered all over, but the only thing is that I want it thin! I have medium-thick hair, but its straight. I just use a hair straightener to make it sleek looking. There is some wave in it though. So I want it really thin looking, where you can see my layers. I see everyone else with this thin hair, and their layers are visible. How do I get mine like this? And how do I keep it STRAIGHT? Hairspray? Thanks so much!