How can i straighten my hair without losing my curl?

i used to have a 3b hair type and i started straightenign it so much that i lost most of my curl. in order to get my curl back i had to cut a lot of it off. its pretty curly now but there are still a few straight pieces. i want to straighten my hair but I'm pretty iffy on it because i'm afraid that if i do it once ill lose my curl for good. Can someone tell me if this is true or any tips on hwo to prevent this?..THANKS! :)