Hi Flashy. Know just what you mean having myself to use straighteners all the time. There are plenty of products on the market. I am using a VO5 'heat protect' spray product at the moment, which (I think) I got from Bodycare. The one before that was a Boots own brand.
You have to look through the shelves for them as there only appears to be one of these products from each manufacturer.
The problem may come if you are using your straighteners again before the next wash and not re-applying; may build up a little particularly if you use hair spray too .. not sure as I wash my hair practically every day. Gotta' laugh ... use shampoo, then conditioner, then the hair protect, then the hair spray !! How I long for straight hair ...
Seems to work anyway .. my hair is in decent condition still.
Best of luck with the swim.