I have long hair (below my shoulder blades) that I straighten with a flat iron about 5 times a week. I haven’t noticed any particular damage, though the ends seem to look a little rough more quickly than before.
I have been using Aussie 3 Minute Miracle conditioner and then Biotera leave-in conditioner (generic for Biolage). My hair is fine and tends towards frizzy under any condition. Do I need to switch to some other products, or will these do fine?
Using a protection product might be good. I use ghd ironing oil (available at several hairdressers and ebay!) everytime I straighten my hair. I just spray it on the ends and it stops my ends getting dry. Its not overly expensive and supermarkets often sell cheaper versions of it. What I also tend to do is use a deep conditioning product once a week and everytime I use it I leave it on for around a half hour and rinse it with cold water (well as cold as I can bear!)
happy straightning!
Have you considered Japanese Straightening? If you’re ever in NYC I can recommend a place. 
As to moisturizers, I like “Potion No. 9” made by Sebastien.
I would love to get Japanese Straightening done! It doesn’t seem to be well-known in Oklahoma yet, so I don’t know how to go about finding a good salon. Unfortunately, I have no plans of traveling to NYC either, so I’m SOL 