How to get more volume with straightened hair

Can anyone tell me how they create more volume when they straighten their hair. I have used volumizing products galore, I have read the tips on the site and when I straighten from the mid shaft down you can still see the waves in my hair. My hair is below my shoulder blades and is fairly thick. I would appreciate any help or ideas that you can give me.It may be that it is just not possible to get much volume with my hair being this long and I don't like to tease my hair. Thank you!