Hello! How are you?
Good luck on going in natural! I have been natural all my life (but I plan on getting a curly perm so lol). But anyways here is my advice I have been through YEARS worth of products all for that coveted curl.
Just one thing, if you don't see curls in your head all ready then you won't get curls without some manipulation. for example, if you hair is like this:http://www.cherrylola.com/images/amino%20acid%20treatment/My%20Texture%20unhandled.png
or even like this (my sisters is like this)http://yougocurl.com/images/nia_front.jpg
You will be able to define your curls. My sister when doing here hair using a shampoo and a good conditioning conditioner. Then when she gets out she adds a leave in condition and uses a curl activator gel in order to help the curls stay. There are many different curl activators out there, a bit of research will help you in that deparment and maybe invest in an anti frizz shampoo or spray.
Also doing styles like twists outs and bantu knots can help with your curly goal, google them for more info.
Lastly if those don't work I heard of some products that should help "enhance and stretch your curls if you have them"http://www.naturalaxer.com/
but if your hair is like this:http://www.ethnic-beauty-central.com/images/AfroBlackBeautymodify.jpg
with no defined curl pattern, more of a z pattern then a S curl, then the only way for curls is either roller setting and night, flexi rods and gel, or twist outs and bantu knots.
Hope this helps!