Heat defense help please :( !?

Hey. I straighten my hair almost everyday with Conair Steam. I recently started using Lee Stafford Poker Straight Flat Iron Protection Shine Mist ( before straightening my hair. But I’m not sure if it really protects my hair from the heat. Should I use more products ? My hair is VERY dry and damaged. And my straightener is giving me a LOT of split ends. 🙁
My friend told me Tresseme Heat defense is really good.
Also, is it better to use serum for heat defense or spray? My hairdresser says serum is better as it spreads evenly.

Thanks a lot. 🙂