Chemical treatments and heat styling destroy hair. Straight haired people use perms and curling irons and curly hair people use relaxers or straight irons. The key is to stop fighting against your hair and learning to work with what it is. Finding a great hair stylist helps a lot too. I haven’t found one near my new place and it’s been a couple years since I’ve had a good cut.
In the 17 years I’ve been coloring my hair, I’ve used the semi-permanent ones that aren’t as damaging. I never use a hair dryer or curling iron anymore and my hair is very shiny and soft.
I’ve heard that Redken All-Soft conditioner is very good. But as others have said, once the damaged is done, you can’t really repair it. If you spend a ton at a salon, they can probably improve it, but the only way to have lasting results is to change your styling habits so the new growth won’t become so damaged.