Sienna Miller

Hey guys.
I recently just got my haircut, I had shorter layers in my hair to encourage waves.
It looked absolutely fantastic when I stepped out of the salon, I asked for it wavy and not too straight and I ADORED IT!!
But now I can't get it the same and it's stressing me out!! I have really good straighteners so I'm using them at the moment, but I don't want it straight.
I was just wondering how I could get my hair to look like Sienna Miller's??? You know, wavy and tousled, doesn't look like she tries too hard with it.
She has layers but when I try and dry mine naturally it just goes bushy and if I use curlers it looks like I've spent ages on it and that's not the look I want to achieve. My friends say that I wouldn' be able to get my hair like hers because hers is quite thin and fine and mines quite thick. Are they right??
Any ideas for how to style my hair would be great, thanks xx