Hi TeaLover,
Just in case you haven’t read it yet … the first place I would start your research is post #1 here which includes links to all the basic information, steps, and guidelines that can help you the most.
There are really only two reliable ways to know whether a mattress is suitable for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) which is your own personal testing of more detailed conversations with a knowledgeable and experienced online manufacturer or retailer (see mattress firmness/comfort levels in post #2 here). “Theory at a distance” or the reviews or experiences of other people are never as reliable as your own personal testing or experience. “Supportive softness” is different for each person but your body will “recognize” what it is for you
The better options and possibilities I’m aware of in the Seattle area are listed in post #2 here.
Phoenix