Need advice for my POOFY hair?

okay, so i have most likely the poofiest hair ever ! So, I want to make it thinner but I dont't know how. I don't want to blowdry, straighten , put products in my hair, or anything like that. My haircut is a shirt shag kinda look. Now, im willing to put any types of oils in my hair....but I don't want it to look greasy. So, any advice ppl?