Hi Kj72,
Thanks for letting us know what you ended up deciding … and congratulations on your new mattress 
You certainly made a great quality/value choice.
All the layers and components in a mattress (including the cover and quilting) will affect the feel and performance of all the other layers and the mattress “as a whole”. The BestMattressEver has a thin layer of polyfoam in the quilting which would provide a slightly softer and more “relaxed” sleeping surface but “most” of what you are feeling would still be from the latex comfort layers although the quilting would feel a little bit less resilient than sleeping directly on a latex comfort layer with a thinner knit cover.
An all latex mattress would typically feel more resilient than a latex/polyfoam hybrid and synthetic Dunlop latex would also feel a little less resilient than Talalay latex or 100% natural Dunlop as well so what you are feeling would be from the “combined effect” of all the materials and components in the mattress.
I would keep in mind that here will be a break in and adjustment period for any new mattress or sleeping system as the mattress loses any of it’s “false firmness” and the cover stretches and loosens a little and the materials settle and your body gets used to a sleeping surface that is different from what it is used to (see post #3 here). This would typically be a few weeks but it can be shorter or longer depending on the specifics of the person and the mattress (higher density materials can take longer) and it can be surprising to many people how much their sleeping experience can change over the course of the first month or so. I would generally suggest sleeping on any new mattress for a few weeks at a minimum Preferably a month or so) whenever possible before deciding on whether it’s a good “match” in terms of comfort, firmness, and PPP and/or deciding to make any changes or additions to your mattress.
If and when the time comes that you decide to add a topper … if the only issue with a mattress is that it is too firm then a good quality topper can certainly be an effective way to add some additional softness, “comfort” and pressure relief to your sleeping system but the only way to know for certain whether a specific mattress/topper combination is a good “match” for you in terms of comfort, firmness, and PPP is based on your own careful testing or personal experience on the mattress/topper combination. If you can’t test the combination in person then there will always be always some risk and uncertainty involved in adding a topper because the specifics of the mattress itself along with your own body type, sleeping position, and preferences can affect which specific topper would be a suitable choice on any specific mattress.
There is more information about choosing a topper in post #2 here and the topper guidelines it links to which along with a conversation with a reliable and knowledgeable supplier (that can provide you with good information about how their toppers compare to each other or to other toppers they are familiar with that are available on the market) can help you use your sleeping experience as a reference point and guideline to help you choose the type, thickness, and firmness for a topper that has the least possible risk and the best chance for success. A good exchange/return policy can also reduce the risk of an online topper purchase so I would make sure you are comfortable with the options you have available after a purchase just in case the topper you choose doesn’t turn out as well as you hoped for.
If a mattress/topper combination turns out to be a good “match” for you in terms of “comfort”, firmness, and PPP then having a separate topper also has the advantage of being able to replace just the topper without replacing the entire mattress if it softens or breaks down before the upper foam layers in the mattress (which is very likely because the upper layers of a sleeping system tend to soften or break down before the deeper layers) or if your needs or preferences change over time. A suitable topper can also help extend the useful life of the mattress underneath it because it will absorb much of the compression forces that can soften or break down the top layers of the mattress underneath it over time.
Phoenix