My hair is never shiny or very soft, how can I get it that way?

So my hair used to be halfway down my back until I cut it just past my shoulders because of split ends (There are still some, I have blow dried my hair a few times but have stopped now) and my hair is rather wavy, more at the front that back, it's more flat there and also my hair is a medium brown colour (naturally it's a bit lighter, my hair darkened while growing up). But the problem is, is that my hair has never been shiny or soft. It's got like layers in it and after the hairdresser straightened it, it was very soft but as soon as I was outside it felt rough and a little bit brittle. My fringe gets greasy often so I get shampoo from Lush to sort of help that out but no matter what shampoo and conditioner I use my hair is never shiny or silky smooth, is it because I don't blow dry it or straighten it? I don't want to damage my hair all I want is soft and shiny hair. I wash my hair now in lukewarm water and for the first time yesterday I washed it with lukewarm water then rinsed over in cold ( I tipped my head back and kept it in one place, it was way too cold to move anywhere else) and nothing really happened, I mean like the top of the back of my head feels kind of smooth but not everywhere else of my hair looks shiny nor smooth. My hair can look quite ratty and frizzy when it's been out in the rain which is unfortunate so I can never win with my hair, I rarely do anything with it because I don't want it damaged and also, I'm rather lazy to do anything exotic I'm just wondering if my hair will never be shiny or soft? If anyone can give me any tips on how to get it shiny and soft I'd greatly appreciate it.