Hi Liquidtheguy,
If you let me know your city or zip code I’d be happy to let you know about any latex options I’m aware of that may be near you but it’s unlikely that you would find a mattress with the same design as one of the Flobeds mattresses and even small differences between mattresses can make a surprising difference in how they feel and compare so local testing on different latex mattresses would only be a very generic guideline and tell you about the “feel” of latex in general but it wouldn’t provide specific information that would tell you what any of the Flobed options would feel like for you.
When you can’t test a mattress in person (or a mattress that has a design that is basically the same) then the best approach to decide on which of the options they have available would have the best chance of success for you would be based on a more detailed conversation with the manufacturer who can help “talk you through” their options and who will know more about “matching” their mattresses to different body types and sleeping positions based on “averages” than anyone else (see mattress firmness/comfort levels in post #2 here).
I certainly wouldn’t go by an automated firmness selector or by your own knowledge alone unless you have enough experience on different latex combinations that you are completely confident that you could choose the layering that was best for you without any additional guidance (which would be rare for a consumer that had never tested a particular online mattress).
What a middle transition layer would feel like for any particular person would depend on their body type, their sleeping positions, and their individual sensitivities along with the specifics of all the other layers and components that are above and below it in a specific mattress because every layer in a mattress will affect how all the other layers feel and respond. This can’t be answered specifically (it would be like trying to describe how something tastes to someone that has no comparable frame of reference) except to say that transition layers affect both pressure relief and support and firmer transition layers would provide a little bit firmer sleeping surface and a little less pressure relief than softer transition layers and they would also have firmer “primary support” than softer transition layers. There is more about primary support, secondary support, and their relationship to pressure relief in post #4 here but in general I would avoid trying to design your own mattress based on specs or get into these types of design specifics or technical information because without a specific frame of reference based on your experience with other similar mattresses you have tried and are very familiar with they will generally lead to information overwhelm and “paralysis by analysis”.
I would talk with the experts (Flobeds) that already know what it would otherwise take you a great deal of time and experience to learn.
Phoenix