Advice for thin and volumeless hair

Hi everyone, I’ve got inspired by some recent hair transformations in this sub and decided to try my luck too :)

My hair is thin, fine and naturally straight.

On the first picture, I’ve just loosened the hair from a hair claw clip and you can see a hint of volume on it (the hair is not brushed though).

Pictures 2 & 3 were taken several hours later, and that is the normal state of my hair – lifeless, stringy and stuck to scalp.

The last picture was fresh after the haircut (I tried to solve this problem by shortening the length, however couldn’t find a styling method that worked for me).

Do you have any tips on how to keep just a little bit of volume throughout the day and prevent the hair from becoming flat?

Thank you!