Hi rceisland,
If you tried to contact them and haven’t heard back in a business day or so then I would call them again. If you emailed them then either your original email or their reply may have gone astray and you may end up waiting for a reply that will never come.
It’s very likely that you could create a better match in terms of PPP if you choose the most suitable latex topper in terms of thickness and firmness but only your own experience can tell you whether a topper you choose in combination with the Nature would be a good match for you in terms of PPP. Whether to exchange your mattress for a different one would depend on the results of your testing on another mattress you were considering exchanging for compared to your testing on the Nature or the Nature/topper combination and which one your testing indicated would likely be a better match for you in terms of PPP (again only your own experience can tell this). The choice of different types of mattresses or materials is a personal preference and would depend on whether you tend to prefer the “feel” of innerspring support cores or latex support cores. There is more about the difference between them in post #28 here but again your own testing and experience is the only reliable way to know which types of mattresses or materials and components you tend to prefer.
The PLB topper would about 15 ILD but I don’t know how it will affect you in terms of PPP. Outside of the topper guidelines I linked in my earlier reply and your own personal testing with this topper on the same mattress in the store, the only reliable way to know whether a specific mattress/topper combination will be a suitable match for you would be based on your personal experience.
Phoenix