Hi jim,
I think one of the most common questions asked on the forum is to recommend a specific mattress based on body type and sleeping position information (and in some cases some other specs) but unfortunately there are so many variables that there is no “formula” that can do this. You can read more about why I don’t do this in post #2 here.
If you have a specific set of “symptoms” on a mattress where all the layers are known then I’m certainly happy to make suggestions or provide some insights based on your actual experience and feedback on a specific mattress but without this type of reference point then the retailer or manufacturer is always in the best position to make the most accurate suggestions in the absence of your own personal testing (assuming they have the knowledge, experience, and enough feedback from their customer base on their mattresses to do so).
The prices for two twin XL Pampers and two 2" toppers (with a foundation?) seems reasonable IMO but I would consider what other options you would have for an exchange if it doesn’t work for you. The topper is 15 ILD which is very soft and this would give you 4" of soft latex in the comfort layers (2" of 21 ILD and another 2" of 15 ILD) which may be a little on the thick/soft side for you, especially with some stomach sleeping, and while it may be OK for your wife in terms of softness with her lighter weight … it may also be on the thick side for her back sleeping.
In the absence of specific testing (which is by far the most accurate way to know what may work best for you) … you are really dependent on the experience and knowledge of the people who are selling you the mattress and in this case it would also be important to me to either know what alternative options you have if it doesn’t work (and any costs involved) or at least be paying a price that justified the risk of buying a mattress where you don’t know how well it may work (compared to other similar mattresses that may offer more options that are available online).
For example … in talking with the person selling the PLB mattress … did they tell you that this would be the option that they believed would work best for you out of the entire PLB lineup. Did they explain why? If they did and you have confidence in their suggestions … I would follow them (knowing they are working with “averages”) as long as you have good options if the suggestions don’t work out. If not … I would either want to test the mattress in person, look for alternatives, or at least confirm that you could exchange it at little or no cost and that you have some good “exchange” possibilities that you would consider if it becomes necessary (such as other PLB choices).
If I was considering an online purchase of a latex mattress … I would be looking at some of the options available in post #21 here before I considered the PLB. I would at least talk with some of them and use their experience and knowledge to your advantage before I chose a mattress that had upper layers that were that thick and soft without a specific reference point or testing it to make sure it would work for you (again unless you are comfortable with the price, risk, and your exchange options).
Phoenix