OK, some miscellaneous thoughts.
(1) Your high stress is coming from your thickness. Beam stress is mc/I. "c" is the distance from the surface to the neutral axis. A thicker beam has a greater "c".
(2) "O-1" is tool steel, right? Not known for its flexibility. I wouldn't expect to find springs made from O-1.
(3) Have you contacted a spring manufacturer? There are several that could be of great assistance.