Hi Gracie1@,
Welcome to the Mattress Forum! 
The Silhouette Marseille Noir (firm) I believe is the same mattress as the Berkeley Ergonomics BE 1500, who most likely produces this item for Ergo Beds under the Silhouette label. The nestled pocketed springs are very high quality (from Germany) and the Talalay latex used is natural. The cover uses organic cotton quilted to Plein Air wool. This item uses good quality and durable materials, and I do think highly of the Berkeley Ergonomics line of mattresses. As you mentioned this model can be made with dual firmnesses, and if Ergo Beds offers the same number of variations as Berkeley Ergonomics, there are four different comfort choices.
I believe the topper you’re describing is also from Berkeley Ergonomics, called the Posturflo. This unique topper uses microsprings and the same Plein Air wool quilted to organic cotton to create an extra layer of plushness when placed upon a mattress. This would also be a good quality and durable item.
The Dreamfoam Ultimate Dreams is a different design from the Silhouette. I’m guessing that you’re referencing the Ultimate Dreams Total Latex, based upon some of your comments. That model uses a latex core (can be natural Dunlop or Talalay at two different firmnesses) and then a 3" layer of Talalay on top of that which can be adjusted/exchanged to different ILDs. The quilt is a layer of organic wool and a thin piece of polyfoam. In a California king mattress this item can be split into different comfort configurations on the left and right side.
Again, I think that you’re actually comparing a Berkeley Ergonomics/Silhouette mattress (not an Obasan) to the Dreamfoam mattress.
Both products use good quality and durable materials. Dreamfoam is known for offering some very good quality components at affordable prices. The Berkeley Ergonomics also uses very high quality materials and imports their unique springs and microsprings from Europe, so the “value” of a mattress purchase from BE includes more than just the material value of the mattress.
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 good news is that you are choosing between “good” and “good” regarding componentry, but there certainly is a difference in that componentry (one item using springs versus a latex support core), so that preference would also enter into your value equation.
If you have more specific questions I’ll do my best to be assistive.
Phoenix