Straight hair!!?

My hair is naturally straight and EXTREAMLY thin. i take showers in the morning, blowdry and then straighten my hair because it gets poofy and a few kinks from blowdrying it. i put a little sunsilk smoothing cream in my hair when its damp. For some reason my hair always poofs up and gets more kinks through out the day at school!! How do i keep my hair straight? Also how can i add volume? Thanks in adcance!!