Full mattress needed!!!!!!!!!!!!!!?

Hey Yahoo! I would very much need some help. I am looking for a Comfy mattress for me, i am thirteen my bed is getting too small, I found a nice bed frame at IKEA but the mattresses there are too expensive! any place i can get a full mattress for less than 200$? the person who can auctually help me with a very detailed answer gets the ten points, plus being rated very highly! Mucho Appreciated!