Hi rikelme,
It really doesn’t compare at all and they are very much apples to oranges comparisons.
The Stearns & Foster is the type of “so called” latex mattress that I would avoid. The “smart latex” is mostly synthetic Dunlop and there is 3.5" of lower quality polyfoam on the top of the mattress which means that you are sleeping primarily on polyfoam not latex. This would be the weal link of the mattress and the reason that so many people see foam softening and body impressions so quickly with many of the Stearns & Foster mattresses. In most cases the foam softening is the issue and the body impressions are usually less than the warranty exclusion. Many people have seen this happen at around the 3 - 5 year mark (and there are several that have talked about it on the forum) but some experience it more quickly. If this happens then you would need to remove the lower quality polyfoam and replace it with higher quality materials (such as latex) or you would have to replace the mattress completely. In a few cases if you are “lucky” then you may qualify for a warranty replacement if the impressions are deep enough (or if you wait long enough) but this is not the norm and then you would be limited to another mattress that most likely had the same issues.
The Custom Sleep Design uses much higher quality materials with no weak links in the mattress, is custom zoned to your body specifications, and they will work with you and replace any of the zones that may be necessary until your mattress is “ideal”. A zoned mattress like this or any mattress really can’t be meaningfully compared to a mattress that uses a completely different designs and materials except to say it is much better quality and value.
Post #1 here and the links it includes has all the basic information, steps and guidelines you would need to make the best possible choices and learn how to avoid mattresses like the Stearns & Foster or any mattress where the information about the quality of the materials inside them are not available to you.
Post #2 here has the better options and possibilities I’m aware of in the San Francisco area and quite a few of these make or sell latex mattresses. I don’t keep a list of mattress styles that each retailer or manufacturer carries on their floor (this would be constantly changing and impossible to keep up with) but some quick research on their sites and a few quick phone calls will identify the ones that carry latex mattresses that you can test.
The list of online manufacturers that are members here (and many of them make and sell latex mattresses of various designs (including designs where you can choose your own layers or components) is in post #21 here.
Phoenix