I've got exactly the same hair as yours and have spent ages trying to achieve this look. Recently realised that effortless is exactly what it is. Use SLS / silicone free shampoo and conditioner. Don't wash it too oftwn and only brush it when it's wet.
The smallest amount of oil to tame it and voila! I also clip a bit off to the side and I can honestly say it had taken me 37 years....but I've finally found a style that I like and it's soooo easy to do.
Pretty rain proof too as that kind of enhances the look.
I love this look, slightly bedhead, a bit fluffy and wavy. My hair is naturally straight at the roots, wavy at the ends and very thick. The style appeals because it looks effortless but I'm not so naive that I'm going to believe that and I was wondering what products or techniques people would recommend to keep my cut looking like this