Hi JAK,
These are all good quality materials and there are no obvious weak links in the mattress although if you are in a higher weight range (more than the low 200’s or so) then I would be somewhat cautious with 3" of 4 lb memory foam in the top layer. You can see the foam density guidelines I would suggest in post #4 here.
There is more about the most important parts of the “value” of a mattress purchase in post #13 here but if you have done some careful testing on the mattress and are confident that it’s a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) and it also compares well to your other finalists based on all the parts of your personal value equation that are most important to you then it would certainly be worth considering.
I also noticed that this mattress isn’t currently on the Ecosus website (although the specs you mentioned are listed on an older website page here) so it may be an old model so I would check the manufacturing date on the law tag to make sure that it is new and was manufactured recently (in the last few months) and that you aren’t purchasing a comfort or a warranty return which would mean that your mattress wouldn’t likely have a warranty.
As you probably know from your reading here … this is much too common with major brand mattresses or with any mattress that uses lower quality materials in the comfort layers or doesn’t disclose the quality of the materials at all. Since your mattress has softened fairly quickly it’s also quite likely that you purchased a mattress that was already close to the edge of being too soft for you when it was new so only a relatively small amount of foam softening was probably enough to take you “over the edge” of the firmness range that is suitable for you in terms of PPP (see post #2 here).
Some local testing on mattresses using the testing guidelines in the tutorial post is always a very good idea so you have a better idea of the types of mattresses and materials that you tend to prefer and you have some good “finalists” to choose between.
I’m looking forward to any comments or questions you may have from your mattress testing and of course finding out what you end up deciding.
Phoenix