T.F.
My daughter (18) and I have long straight dark hair. We only trim and use one step color ONLY by a professional.... never, EVER a DIY.
We routinely use coconut oil for conditioner. We use in on the ends, not scalp. Leave it overnight. We both have very healthy, shiny tresses and I swear by Coconut oil.
A jar is less than $10 found in the oil aisle at the grocery. It is in solid form but when it gets on your hands, it melts. Don't use too much at once, moderately or you'll have to use a clarifying shampoo to get the excess out.
We typically shampoo every other day. I use the hair dryer for less than 5 minutes... We let our hair get almost dry by air drying first and limit the heat we put on it. We don't do curlers. She will only use the Chi straightener for special occasions.