Hi droidx.
As always with any mattress, I’d make sure to first check with the manufacturer of the mattress you are considering to ensure that your current foundation meets the manufacturer’s warranty criteria. I am not very sure what type of “box spring” you own but if it is the metal semi-flex foundation that Simmons provided with their mattresses a decade ago I’d make sure to check that it is perfectly flat and that it has no dips or flexing that can negatively affect the performance and of your new mattress.
Generally, a foam mattress with a polyfoam support core will do best with a firm, flat, and evenly supportive support surface underneath it that has minimal to no flex under the mattress. In your case for a king size, the foundation would need at least one center support beam that has good support to the floor to prevent any sagging in the middle of the mattress. The components (either a bedframe and foundation or a platform bed) need to be strong and durable enough to support the weight of the mattress and the people sleeping on it without some of the parts bending, sagging, shifting, or breaking with extended use. The support surface under the mattress (which may be a solid surface, slats or a steel or wire grid) should have enough surface area to prevent the mattress from sagging through any gaps or spaces in the support surface over time but still allow some airflow under the mattress. If a foundation has a slatted surface then I would suggest that the gaps between any slats are no more than about 5" (with 1 x 3 slats) although I would strongly suggest 4" or less which would be better yet.
While an “active” boxspring (such as the one used for an innerspring) wouldn’t damage the foam, and as long as the supportive surface is even, in most cases an “active” boxspring under a foam mattress will detract from the performance of the foam (it will compress when it shouldn’t) and detract from the alignment and support of the mattress. … is certainly doesn’t allow the foam to live up to its best potential. An “active” boxspring it is not the ideal base for an all foam mattress in the majority of cases as the “active” part of it is usually designed to aid an innerspring mattress. There’s much more information about the functions of foundations, active slat systems and actual box springs in the foundation thread here. With most modern mattresses, the bottom piece of the mattress set is a foundation that does not flex.
You are looking at two different mattress types and design with different “feels”, different characteristics, and different firmness levels. Every individual layer and component in a mattress (including the cover and any quilting material) will affect the feel and response of every other layer and component both above and below it and the mattress “as a whole” so each mattress category will generally include some mattresses that have a design that will be a good “match” for you in terms of “comfort”, firmness, and PPP and others that use the same type of materials and components and are in the same category and may be just as durable but have a different design or firmness level that may be completely unsuitable for you to sleep on … even if it uses the same general type of materials and components.
Generally the best way to compare two mattresses from different manufacturers which are in the same mattress category and have a similar construction, would be to place a call to the manufacturer themselves and ask about how their product would compare to the other one (in your case the one you currently own) They would have much more experience with their own product and similar competitor products and usually base their assessment on their direct experience and on customer feedback … that could be more helpful to you.
While DF is not a member of our site, generally each time you wish to check if a specific company is a TMU trusted member you can always check the most up to date membership listing here.
Phoenix