Hi Xyth,
The thickness of the foam on top of the coils has little to nothing to do with the quality or durability of the mattress … only whether it would be a suitable “match” for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences). There are no lower quality materials or “weak links” in any of the mattresses you are considering.
In very general terms side sleepers tend to need a thicker/softer comfort layer than back sleepers and stomach sleepers tend to need the thinnest comfort layers of all but these are only very generic guidelines and when it gets down to the specifics that would work well for any particular person then only your own testing or personal experience can tell you whether any mattress is a suitable “match” for your body type and sleeping style.
You are the only one that can feel what you feel on a mattress and there are too many unknowns, variables, and personal preferences involved to use a formula or for anyone to be able to predict or make a specific suggestion or recommendation about which mattress or combination of materials and components would be the best “match” for you in terms of PPP or how a mattress will “feel” based on specs (either yours or a mattress) or “theory at a distance” that can possibly be more accurate than your own careful testing or personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
When you can’t test a mattress in person then the most reliable source of guidance is always a more detailed conversation with a knowledgeable and experienced retailer or manufacturer that has your best interests at heart and who can help “talk you through” the specifics of their mattresses and the options they have available that may be the best “match” for you based on the information you provide them, any local testing you have done or mattresses you have slept on and liked that they are familiar with, and the “averages” of other customers that are similar to you. They will know more about “matching” their specific mattress designs to different body types, sleeping positions, and preferences (or even to other mattresses that they are familiar with) than anyone else.
An online choice is always a higher risk purchase because you won’t know whether it’s a good match for you in terms of PPP until you sleep on it. There is also more about the different ways to choose a mattress (either locally or online) that is the most suitable “match” for your specific needs and preferences and that can help with how to identify and minimize the risks of making a choice that doesn’t turn out as well as you hoped for that are involved in each of them in post #2 here.
When you are making an online purchase that you haven’t tried in person then the options you have after a purchase to exchange or return the mattress or make changes in individual layers to fine tune the comfort and support of the mattress (and the costs involved) is the most effective way to reduce the risks involved and for most people would become a much more important part of the “value” of your purchase so I would make sure you are comfortable with the options they provide after a purchase “just in case”.
I would also keep in mind that you can always add additional softness and pressure relief to a mattress by adding a topper but it’s much more difficult to firm up a mattress that is too soft because this would normally require removing and replacing the layers or components in the mattress that are either too thick or too soft.
The tutorial post includes several links to some of the better online options I’m aware of (in the optional online step) and if you let me know your city or zip code I’d also be happy to let you know about the better options or possibilities I’m aware of that are close to you as well.
Phoenix