Hi scoaste,
I would advise you to not try to predict how you will feel or react to a mattress from a number scale, as that has nothing to do with you or your current mattress, and only represents one brand’s attempt to rate their own mattresses relative to one another. Nothing can possibly be more accurate than your own careful and objective testing (using the testing guidelines in the tutorial post) which is always the most reliable way to predict which mattress will be the best match for you in terms of PPP (Posture and alignment, Pressure relief, and your Personal preferences) (see mattress firmness/comfort levels in post #2 here).
As you seem to be convinced that you need something even softer than your current mattress, make sure to become familiar with any potential return/exchange policy of any brand/manufacturer you are considering, should things unfortunately not turn out as you had hoped.
Phoenix