My hair is not nearly as straight as yours, but it is very fine. lately I have discovered two things that help- Pantene pro-V sheer volume shampoo, and not combing it throughout the day. I have actually managed to keep my hair sort of long and not looking totally flat and dead!

and for the record, I totally think you should try cutting your hair, at worst it will grow back, at best you will have a gorgeous new look :)