Hi gehinpa,
Out of the mattresses you tested the only one that would provide a reference point where the layers are known is the PLB Nature. Assuming that it was the natural (not the all natural) then you can find the details of the layers here which you can use as a reference point in your conversations with each of the manufacturers you are considering (outside of specific local testing … they are the best source of guidance for your comfort choices for the mattresses they make). Of course the layer thickness is different so they would have to try to “translate” which of their designs may come the closest based on an “educated guess” (and this could vary for different people depending on how they interact with the mattress so it would be a “best guess” based on their experience).
It may also be worth trying a PLB Beautiful which is softer than the Nature if they are available in your area because it has layers that more closely approximate the mattresses you are considering (the top 2 layers are both 3"). The PLB retail finder is here so you can search for retail stores in your area that may carry them.
Regarding sleeping temperature … post #2 here and post #29 here may be helpful and outline many of the “interactive” factors that can affect the sleeping temperature of a mattress. As you can see … even something as seemingly “innocent” as your choice of mattress protector or sheets … for some people that are more sensitive to heat … can negate most of the benefits of a mattress that would otherwise sleep cooler.
With the specific medical needs of your daughter and her more “curvy” shape … there is some risk involved in “fitting” her to an online choice because “theory” is only based on averages and because each person is individual and there are many people who don’t fit the “average range”. because of this and the probability that her needs are much more specific than most people, I would lean towards a choice where you have more ways to re-arrange or fine tune your choices either with the individual layers and/or with the addition of the topper you have. This means that I would certainly lean towards the Alexis with two customizable layers over a mattress where only the comfort layer can be exchanged. While the polyfoam base layer in the Alexis is the one that will likely have the least effect with her lighter weight … having a firm latex base layer does allow you to “move it up” one level if you need firmer support under a comfort layer so a third layer of latex provides further options to customize yet should you need them. The “value” of these options and any tradeoffs in price that are involved are of course part of each person’s personal value equation.
How you approach a manufacturer or retailer in your conversations with them may also affect their willingness to “guess” which layering option may be best for you because if they sense that you believe they have the ability to provide some type of assurance that their “best guess” will be right or that you believe they are responsible for your comfort choices when it’s only a “best guess” based on experience and averages (that may or may not fit your needs and preferences exactly) then they will be much less likely to take the risk of “guessing” for a customer that puts the responsibility of a comfort choice on the manufacturer or retailer or who may “rate” the mattress in a review based on its subjective comfort when in fact the only thing they can truly speak to is the quality of the materials, what “most people” do best with, and the options you have to “fine tune” your choice in the direction of your ideal layering.
It helps if you let them know in other words that you realize that their guidance is based on averages and not on specific knowledge of your circumstances or conditions that can change what what may be best for any individual person. Telling them that …
“I know that you can’t possibly know what is best for me except based on the averages of other people and that I may not fit these averages but your experience and guidance would be very welcome even though I know my choices are my own responsibility”
may lead to more specific guidance than if they sense that you think they have the ability to provide specific personalized “answers” for your best choices and that they are dealing with a customer that will hold them “accountable” for their comfort choices … especially if the circumstances are more challenging.
There may also be local options available that may have good value that you could test in person or perhaps allow you to test mattresses that are closer to the ones you are considering that you can use as a more equivalent “guideline” (that would be easier to “translate” into one of the mattresses you are considering). If you let me know the city or zip where you live I’d be happy to let you know of any local options I’m aware of.
Overall … I believe that careful and objective personal testing and experience is the most accurate way to choose a mattress in most cases and that the “next best” way is to use the results of your local testing as part of a more detailed conversation with a retailer or manufacturer you are considering so you can use their insights and the “averages” of their customers to help you make the choice you believe would be best for you or that at least has the best odds of success either in a “standard” configuration or by re-arranging or exchanging a layer.
In the end … final choices with an online purchase will always be based on your level of confidence that your choices will be as close as possible to your ideal or that the options you have after a purchase can get close enough to your “ideal layering” and will involve your own “best guess” or “educated intuition” based on your conversations.
Phoenix