HI karenmh3,
Welcome to the Mattress Forum! 
The foams used in each mattress are:
Saatva ZenHaven (from top, flippable)
1.5" 5-Zone Talalay (N2 – 20-25 ILD)
3" Talalay (N4 – 30-35 ILD)
3" Talalay (N3 – 25-30 ILD)
1.5" 5-Zone Talalay (N1 – 14-20 ILD)
The Talalay latex is 100% NR from Talalay Global.
This product is not customizable, but you may flip the product over the achieve a slightly different feel. They rate their “Gentle Firm” side as being 18% firmer than the “Luxury Plush” side.
There is a 1" wool layer on each side listed as organic and the cover uses organic cotton.
They offer a 75 day home trial, when the mattress can be returned, less the original delivery fee.
Sleep on Latex offers multiple configurations using either Dunlop, Talalay or a combination of both. Their Talalay is from Radium and their Dunlop is from Lien A. Both their Dunlop and Talalay are 100% NR. A listing of their densities and ILD can be found in a chart under Specifications of our Latex on this page. Their cover uses organic cotton and Joma wool. Their mattresses are component configurable systems.
They offer a 60 day comfort layer exchange program and a 120 night comfort trial return program, less return shipping fees.
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I think you may have some of your information mixed up a little, as when you choose the configuration of the Foam Sweet Foam mattress you can choose all Talalay, all Dunlop or a combination of both. I would phone them and use their advice regarding a mattress and configuration that they think would work best for you. Foam Sweet Foam is a member of this site which means that I think very highly of them and that I believe that they compete well with the best in the industry in terms of their quality, value, service, knowledge, and transparency. They are extremely knowledgeable about latex and different configurations.
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All latex is a highly durable material, so the biggest concern I would have is making sure that whatever customizable system you chose from Foam Sweet Foam was more appropriate for someone with a higher BMI. The Zenhaven doesn’t have a configurable option, but you could flip it to the firmer side and see if it worked well enough for you.
There is more about the 3 most important parts of the “value” of a mattress purchase in post #13 here which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on suitability, durability, and all the other parts of your personal value equation that are most important to you (including the price of course and the options you have available after a purchase if your choice doesn’t turn out as well as you hoped for).
While price is certainly important of course, the “value” of a mattress purchase is what is most important and price is just one of many factors that can affect the “value” of a mattress purchase. There isn’t a “formula” that can be used to assess or “calculate” the value of a mattress because there are so many different variables and criteria involved that can affect the price of a mattress that can each be more or less important to some people and not to others who may have completely different criteria or definitions of “value”. The value of a mattress purchase is also relative to how a mattress compares to the other finalists you are considering or to other mattresses that are available to you in your area (or online if you are also considering online options). There are many reasons that a mattress that may be “good value” for one person or in one area of the country may not be good value for someone else that has very different needs and preferences or that lives in a different area.
The biggest difference between these two products is the ability to customize the Foam Sweet Foam, versus being locked into one configuration (with two different sides) in the Zenhaven. Otherwise, you’re dealing with good quality componentry in both.
Phoenix