Hi dstefano,
I would be very careful which “opinions” you choose to believe … particularly when there are no facts behind it to validate them or when they come from someone that sells the particular mattress that they say is “better”.
The layers are enclosed with a fabric compartment with a zipper that zips tightly shut and if the zipper was removed and the enclosure was sewn shut instead the materials inside it would be the same and would be no more or less durable or likely to “fall apart”. There are many pillowtop mattresses that also have a separate enclosure for the top layers of foam that don’t have a zipper and it’s not the enclosure that determines whether it will soften, degrade, or 'fall apart" but the quality of the materials inside it. The advantage of having removable layers is that you can make changes to the mattress either initially or down the road (if the materials in the comfort layers soften more quickly) without having to replace the whole mattress.
I would trust your actual research over opinions that aren’t based in fact. It’s always helpful to ask “why” someone believes what they believe to see if it’s just marketing or competitive salesmanship or whether there are actually facts behind the opinions. I would also make a preference choice between memory foam and latex so you can narrow down your options here as well.
The most effective way to make your choice that I know of is to just follow the steps that are outlined in the “read first” post I linked earlier and to avoid the tendency to overanalyze or accept unvalidated opinions as fact. If you shop at 100 different stores you will probably find 100 different opinions but most of the better ones will go through the pros and cons of each choice rather than only promoting what they happen to sell. The key is to test a mattress for PPP (Posture and alignment, Pressure relief, and Personal preferences) either with the intent to purchase it or as a guideline for an online purchase … to make sure you know the quality and durability of the materials inside a mattress (so you can make meaningful comparisons in terms of durability and value) … and to assess all the pros and cons of each choice based on your own personal value equation.
If you do choose to make an online purchase for the sake of “value” compared to what is available locally then I would also make sure that you have a more detailed conversation with any manufacturer or retailer you are considering on the phone (not just email) to help you make your comfort choices and also take all of the options you have after your purchase into account (such as exchanging or returning the mattress or individual layers and any costs involved) so if you make a comfort choice that isn’t ideal you know ahead of time what your risks and options are and any costs involved.
If you narrow your choices down to the “one” you would buy at each retailer or manufacturer either locally or online (the one you would choose if you could only shop there) then your final choice will be much easier.
Phoenix