Sorry this is so long ๐
I have straight, fine hair and I currently use the Herbal Essences rose hip shampoo. It's really great at adding shine and making my hair smooth and soft (also smells yummy ๐). I've also used the Maui Moisture lightweight hydration shampoo (the pink bottle) and liked it.
Another thing that has been a game-changer for my hair is double shampooing! Because my hair is so straight and fine, it gets oily very quickly. I discovered double shampooing recently (which is just shampooing twice) and it gives my hair a little volume and it can last longer without looking greasy. I do every other day!
For conditioners/leave-ins I highly recommend anything with jojoba oil! My hair LOVES it and since I'm assuming we have similar hair types yours might love it too.
This is an add-on but the Tsubaki Fino hair mask is affordable and makes my hair sooooo shiny!