Continue using a thermal protector before you blow dry your hair and before you run the flat iron throuh your hair. I like Paul Mitchell's Heat Seal spray. I've never tried the Tigi one you use, though. Then after the thermal spray, try a silicone-enhanced shine spray (I like Paul Mitchell The Shine) before you flat iron your hair as well.
After you've flat ironed, try smoothing a silicone serum or gloss drops on your hair (mostly near the ends where most of the damage is). Then run the flat iron through your hair once more. The silicones help close and smooth the cuticle of the hair so your hair will look and feel more smooth.
Also, use a deep conditioner once a week to help repair the damage that's already been done.