This stuff is amazing for your hair, it can be a little pricey though. I buy mine at amazon.com. its called ITS A 10 by It's a 10: MIRACLE LEAVE IN PRODUCT. another option or rather use both that's what I do. I use the 10 product before I dry my hair and then after it's dried before I straighten it I use a small dime size dab of John Frieda Frizz ease hair serum for thermal protection (its the orange bottle). use more if your hair is thicker, just try not to add too much to the roots or top of your head or your hair will look oily.
there are sprays you buy that are like a barrier. I use a thermal protector from GHD but there's no way to avoid doing damage to your hair, especially if you do it everyday. also, buy a deep conditioner and put it on your roots once per week for like 15 minutes.
Just go to your local drugstore - or anywhere that sells hair products. Nearly every brand has some kind of heat protector/ straightening cream. If you straighten it everyday though, your hair will be damaged more quickly no matter what products you use.