On your back and stomach your spine should be supported in its natural "S" curve and on your side it
should be completely straight ... including your neck. To test for "straightness" on your side,  your
partner can use the yardstick or broom handle as a reference and see how your spine looks in
comparison. On your back and stomach they should squat down and take a look from the side to make
sure the "S" curve is similar to when you are standing. If it seems that a part of you is down too low, try
putting a thin pillow under that area to see if improves your alignment. If it does, you know that part of
you needs to "come up". You're not looking for perfection to the millimeter since your body has some
flexibility, but you also don't want any unusual "bends" that are clearly noticeable.
Now lie on your back if you sleep in that position. Once again try to sense any areas of strain along your
back or neck by lying quietly and listening once again to your body. Pay particular attention to any gaps
in the lumbar area, how deeply the pelvis is sinking down, and whether it seems the upper back is being
held up too high.
A mattress core that is too firm can lead to "gaps" in the recessed areas of your body. This means poor
support. You need to "sink down" deeper in one or more areas. On the other hand a mattress core that is
too soft for you will let parts of you sink in too far (especially your hips) and cause strain somewhere along
your spine as you will not be sleeping in your natural "S" alignment. You need a firmer support layer that
will bring the "offending" part up. This too is poor support. Each mattress you test should move you closer
to knowing what works best for you, and what you should test next.