the current Herbal Essences products are very good.......I use the Shampoo and conditioner in the pink bottle and they are excellent.......my hair seems to stay straighter for longer, meaning I don't have to use the starighteners so often, but I would echo what Kate says......if using heat on your hair is essential to you, then you must use a heat protector spray.....I use Tresemme.....it isn't the cheapest product, but i find it works best for me.
The other thing you could try is to give yourself a hot oil treatment......and you can use olive oil for this...it doesn't have to be the extra virgin
........I warm a couple of tablespoons of oil and put it through my hair....wrap my head in cling film and then put a towel over, leave it for at least half an hour (longer if you can) and then wash the oil out......it may take two applications of shampoo to do it....but then you should be left with lovely silky locks.