Are you doing any protein treatments? Be careful of leaving protein treatments on too long because they can end up doing the reverse of what you want, but if you only leave the protein on for about 2 minutes it will help strengthen your hair.
You MUST follow a protein treatment right away with a deep treatment. lCurlisto makes a deep threatment (Deep therapy masque) that you only need to leave on 3-8 minutes in the shower. Even if you don't do any protein treatments, you should still do deep treatments at least twice a month if you are straightening your hair. If you leave the protein on 2 minutes and the deep treatment on 5 you've only added 7 minutes to your routine - twice a month.
I straighten using rollers because I find it is less damaging to my hair. I use magnetic or wire rollers with the brush part taken out. Velcro gets snarled in my hair so I don't use those.
If you can straighten using rollers you will get a soft wavy set but it won't be stick straight. I used to blow dry every day, but gave that up for curls and for roller sets because my hair was falling out from all the blow drying damage.
If your hair becomes damaged it will show more frizz and split ends.
I've found Infusium 23 to be a great leave in. Use just a little. It's not creamy - more like a setting lotion but has very little hold. It does have cones though. It makes my hair smooth.
I hope this is helpful and that you enjoy your pretty straightened look - it can certainly look as pretty as curls and in some cases prettier, if you maintain your hair well. Good luck!
2/c. Coarse hair med. density.
Protein sensitive but can use occasionally
Highly porous. Color over grey.
Best 1st day method: Smasters!
Stylers: Mix Curls in a Bottle into everything for shine. Terrible pj
Sometimes try roller sets or use a curling brush - classic glamor. Every day is a gift
I straighten...still trying to get it right, but I definitely know the signs of damage. Look for split ends, transparent strands, white beads on the ends of strands (looks sort of like strands that shed at the root, only it's at the other end), and rough frizzies. Also if your hair sounds like crinkling plastic wrap when you brush/comb it or rub it b/w your fingers, it's in dire need of moisture, ASAP.
curlypearl has some really good ideas on how to avoid it. Good luck!