My hair is curly in the front and wavy/straight in the back?

Ok, so I have really curly (a little longer than shoulder-length) hair near my face and on the sides of my head (like, ringlets), but in the back, it's totally different. The bottom layer of hair is like stick-straight and really thin, and the layers on top are just kind of wavyish. I take showers in the morning and let my hair air-dry; I currently don't put any product in it. I've tried using "curl-enhancing sprays", scrunching my hair and everything, and although that looks ok in the front, the back just stays ugly. Do you have any suggestions as to how I could get those hairs in the back to the same pretty curls as in the front? Also, I'd rather not use any heat (curling iron, etc). Thanks!