Hi staceyneil,
The thickness of a mattress or the number of layers or the thickness of any individual layers inside it is really just a side effect of the design and the design goals of a mattress and is also only one of many variables that can affect the feel and performance of a mattress relative to any particular person and by itself isn’t particularly meaningful (see post #2 here). In some cases higher weight ranges (or a higher BMI) will sometimes do better with a mattress that is thicker than lower weight ranges or a lower BMI (see post #14 here for more about the effect of thickness) but even this depends more on the specific design and combination of materials in the mattress and on how well your testing or personal experience indicates the mattress “as a whole” matches your specific needs and preferences in terms of comfort, firmness, and PPP (Posture and alignment, Pressure relief, and your own Personal preferences) than it does on just the thickness itself.
The only way to know which one would be “best” for you (regardless of whether it would be “best” for someone else) in terms of “comfort”, firmness, and PPP will be based on your own careful testing and personal experience.
There is also more about the pros and cons of a component mattress with a zip cover and loose layers that can be rearranged or exchanged vs a finished mattress with glued layers in post #15 here and post #2 here that may be helpful as well.
Subject to first confirming that any retailer or manufacturer on the list you wish to deal with is completely transparent (see this article) and to making sure that any mattress you are considering meets the quality/value guidelines here … the better options or possibilities I’m aware of in and around the Maine area are listed in post #2 here.
Portland Mattress Makers and Spindle would certainly both be well worth including in your research,
Phoenix