Hi teknikAL,
You’ve probably already seen this but some of the better options or “possibilities” in your area I’m aware of (depending on their willingness and ability to disclose all the materials inside their mattresses) are in post #2 here and includes Home Green Home.
It makes perfect sense to me. Another member described the differences well in their post here and there is more discussion in the rest of the thread as well about the effects of having a separate topper.
One of the reasons is that a separate topper has more freedom to move and respond independently and “acts” softer because it is less constrained by the other layers and components of the mattress than the same layer inside the cover. The other reason is that all other things being equal (layer ILD’s and type of latex) that a thicker mattress will also feel softer and have a greater ability to adapt to different body types and sleeping positions. There is more about this in post #14 here.
It’s also good to see that you are looking at all the parts of a mattress purchase as part of your personal value equation because less expensive is not always the “best value” depending on all the objective, subjective, and intangible criteria that are most important to you.
Thanks for your feedback.
Phoenix