Hi pechelman,
Welcome to our Mattress Forum!
Thanks for the useful details, history, and stats. I am sorry to hear that the new mattress from one of our Trusted Members seems to not work out for you.
As Jeremy at Sleep EZ mentioned… with the sales going on and possibly reduced staff over the Memorial Day long weekend, customer service is usually on the back burner. I am hoping that you reached out to the seller today and had a chance to discuss your situation.
Your approach and research lead to a good durable product that meets many of your stated criteria which would typically have good chances of success. Even with the best research and guidance sometimes there is something that escaped attention as there are too many unknowns and interconnected variables involved that are unique to each person … if a mattress is well inside a suitable comfort/support range and isn’t close to the edge of being too soft when it is new (see post #2 , in which case you’d need to do a bit of detective work.
Whenever someone comments about a mattress having a sag or a “hammock feeling” for a new mattress, I always suggest a “ground up” assessment to make sure that there is nothing under the mattress that may be contributing to the issue. The first thing I would check is if somehow the foundation bends under the weight of the mattress and the people sleeping on it. The spacing between slats seems adequate but from your description, I am not able to determine if the foundation has appropriate center support especially for a king mattress. To eliminate the foundation as the problem I’d place the mattress on the floor and see if it makes any difference. If it doesn’t make any difference at all then the chances are it’s your mattress. If it does make some difference then the chances are it would be your support system. A good support system should provide similar support under a mattress as the floor. Without proper support, the bed will sink and soften and not perform as designed.
I would also call the seller to make sure that the foundation you have meets their minimum requirements. I would not assume that your current foundation is compatible with your new mattress. A 9" all-latex mattress is significantly heavier and more “active” than most other mattress types. Pairing an improper foundation or frame will void the warranty and any comfort adjustment terms.
You may also want to eliminate the possibility of any defective layers by checking each of the latex layers by putting them (individual layers) on the floor and then either running a string from edge to edge or use a straight edge (such as a broom handle) across the layers and then measuring the depth of any visible impression from the bottom of the straight edge or from the string. While it would be unusual … if either of your latex layers is defective and there are visible impressions that are deeper than they should be then I would certainly talk to the seller about a warranty claim.
If the mattress behaves the same both on the floor and on top of the foundation then the issue is most likely a comfort issue (unless any of the latex layers are defective). As you have several layers available from your two twins, I would switch some of the layers around and see which comfort/support configuration works best for one individual sleeper at a time. (Hopefully, you have some seeping alternatives available for the other sleeper)
Let us know if you managed to contact the seller and the results of any of the experiments suggested above.
Phoenix