Hi LibbyMark,
The better options or possibilities I’m aware of in and around the Philadelphia/Wilmington/Trenton areas (subject to making sure that any mattress you are considering meet the quality/value guidelines here) are listed in post #4 here.
There is more about the pros and cons of a single 6" core vs two separate 3" layers in post #2 here.
What you are describing is called zoning where a mattress is designed with different firmness levels under different areas of the body.
While zoning may not be as important with latex (see post #7 here) even with latex zoning systems can sometimes be useful and worth considering for people that have more difficulty finding a mattress with the right “balance” between comfort/pressure relief (under the shoulders especially) and support/alignment (under the hips/pelvis especially) or who have more challenging circumstances or sensitivities, body types that are more difficult to “match” to a mattress, more complex medical issues, or who have a history of having more difficulty in finding a mattress that works well for them. There is more about zoning in this article and in post #11 here and the additional posts it links to but the only way to know whether any specific mattress (zoned or otherwise) will be a good “match” for you in terms of PPP will be based on your careful testing and personal experience.
Phoenix