Hi jwjojo,
Welcome to the Mattress Forum! 
Unfortunately, it would be an impossibility for any one person to maintain a listing of the tens of thousands of mattresses produced domestically and have a database of the specifications of each model (much of which isn’t shared by many manufacturers) and relate what might be available that is “similar” to what you’re trying to match in an ever-changing environment. And I also wouldn’t have knowledge of the level of flexibility of each item – that is a question best left to the specific retailer or something that you could test in person.
However, there is information in post #9 here about the different ways that one mattress can “match” or “approximate” another one. Every layer and component in a mattress (including the cover and any quilting materials) will affect the feel and performance of every other layer and component and the mattress “as a whole” so unless you are able to find another mattress that uses exactly the same type of materials, components, cover and quilting, layer thicknesses, layer firmnesses, and overall design (which would be fairly unlikely), then there really isn’t a reliable way to match one mattress to another one in terms of “comfort”, firmness, and PPP (Posture and alignment, Pressure relief, and your Personal preferences) based on the specifications of the mattresses (even assuming that you can find out all the specifications you would need for both mattresses you are comparing in the first place).
When comparing mattresses, you would want to begin by learning the information listed here so you can compare the quality of the materials and components to the durability guidelines here to make sure there are no lower quality materials or weak links in a mattress that would be a cause for concern relative to the durability and useful life of a mattress before making any purchase. You could then use this as a guideline of attempting to find an item approximating what you are attempting to replicate. Of course, nothing can replace your own personal testing in a showroom and also it would allow you to test for the level of flexibility that you might need, so in this case you might be best served by staying more local in your comparisons.
If you like, you can read more about Charles P Rogers in post #34 here (and the rest of the topic) and in this topic and this topic as well and a forum search on Charles P Rogers (you can just click the link) will bring up more comments and feedback about them as well. There have been some “bits and pieces” of specifications provided to site members before on their mattresses (and some have had some good quality materials), but some of it has been conflicting and some of it is a few years old, so just to be safe you’d want to confirm the specifications of any model you were considering or trying to replicate. You can also read a bit more about TOBG here, and gather a bit of information that might explain why CPR is so highly recommended on his site.
Phoenix