I am the same my lashes are long and straight. You have to use waterproof mascara to keep the curl. I slightly heat my eyelash curlers with my hair dryer, be careful they only need a couple if seconds. I then use a waterproof mascara which holds the curl in place. No water based mascaras will hold the curl in place or curl dead straight lashes, believe me I have, not even benefit roller lash. DIOR waterproof mascaras are amazing but if you want something fab but cheaper maybelline do some fab ones too.
I'm going to apologise in advance because this is not a product debenhams sells (and I actively avoid recommending non debenhams products here) .. But this stuff has been a game change for me!
It's called Kanebo Kate lash maximiser. I ordered from eBay after reading reviews on MakeupAlley and it comes from Japan but soooo worth it!!
I absolutely love my chanel me volume mascara but it just doesn't hold a curl even with heated eyelash curlers! This is a mascara primer which holds a curl for me all day and even makes my cheaper mascaras look better!