What shampoo should I use?

I have VERY thick hair, and its almost to my bum. It's always frizzy and I'm looking for shiny, soft, frizz-free hair. I do get split ends frequently. Please don't tell me to use many products because I've heard that so many products do more damage than good. Please help me! (I've tried a tbs of olive oil with almost no success. Should I use more?)