If you have GHD type straighteners you can use them to add beachy-style waves. Search YouTube for instructional videos; it does take a bit of practice though. My hair is a similar length to yours and sometimes I get my daughter to plait it while wet for a wavy effect.
My hair is naturally quite wavy. I used to straighten every day but have had it more curly/tousled for a couple of years and been growing it longer. I started by having it layered - if hair is the same length it tends to "droop" quicker I find. So a really good haircut is essential. My hairdresser doesn't use scissors - uses a blade. Still got a Jennifer Aniston kind of cut, but more messy and unstructured, ikywim. If you already have a kink to your hair you should be able to bring it out without having to use tongs. I use quite a lot of products but the end result is still natural. Start with Shu Uemura hair oil and Shu Uemura Kaze Wave mousse on wet hair. MOP texture spray on damp hair and let it dry naturally just scrunching it now and then. Then when it's nearly dry I squash in soft curl cream by Tony and Guy and if I want extra firm hold I mix the cream with some hairspray in my hand before squashing it in. Good luck! If you persevere you'll never look back and when you get the knack of it it's so much easier and faster than straighteners every day! Sorry, can't link - but this woman is my absolute style icon with the best hair ever: If you can't see this then google Jessie Baylin for ultimate beachy tousled hair
What happens if you sleep on it wet/damp? My hair has a natural wave in it so I normally wash it before bed, scrunch a bit of mousse through it if I remember, comb it out and then sleep on it and in the morning it is all bouncy and curly. Might be worth a shot in case yours is the same?
Bumble and Bumble Brilliantine is fab for tousled hair once you've done the bulk of the styling