I suggest you go into SpaceClaim and use Split Body to split the thin spring section from the thick base, then Suppress for Physics the thick base. On the Prepare tab, use the Midsurface button to convert that thin spring body to a surface, then close SpaceClaim.

In Mechanical, apply Fixed Support to the two edges of the surface were the thick base used to be. This shell model will solve much faster than the solid model and have more accurate stress results.

If you don't want to go to a shell element, splitting the body will allow a sweep hex mesh through the thickness of the thin spring and you would want 4 elements through the thickness.