I have very fine, silky, flat hair that if left to itself is limp, flyaway and lifeless. With aging my hair now has two textures - the coloured hair is as before but the white hair is much coarser although still very straight and flat.
My hair is also much dryer than it was in my youth, when it was rather greasy.
I’ve tried loads of different brands of shampoo and conditioner over the years, all unsatisfactory in the end. Except for Aussie which is brilliant! I use Aussie shampoo and conditioner every 2nd or 3rd day, with occasional use of the 3 Minute Miracle conditioner if my hair is especially dry or hopeless. These products don’t weigh down the hair at all, they leave it lovely and soft and shiny. I also use a hot brush hairdryer to add volume as I dry and have just bought a hot styling brush to use between washes instead of tongs. None of these things give me ‘big hair’ but they do add some volume and body, which makes styling easier, and the hot brushes are much kinder to the hair than tongs. And Elnette hairspray helps to maintain it all day.
Another brand which I use occasionally is Lush - they do a shampoo called Big which is brilliant for fine flat hair, every bit as good as Aussie and does add some volume. They also do conditioners - I’ve used Veganese several times and find it good, although I have to use a little more of it than the Aussie conditioner.
I recommend both Lush and Aussie.