My aunt had a herniated disk in her lower back, too. She got a Japanese-style futon because she heard that it might improve her condition. Well, she said that she woke up without pain for the first six months of using it. But then one morning she woke up with the same pain again, and she continued to wake up with the pain each and every morning thereafter.
She said that while it never worsened her condition, it never really improved it either. She said that she would not spend the money on the futon if she had it to do all over again.