Hi frederixx,
The best place to start your research is the mattress shopping tutorial here which has all the basic information, steps, and guidelines that can help you make the best possible choice … and know how and why to avoid the worst ones.
Almost all mattresses contain some type of foam material (latex foam, memory foam, polyfoam) as either part or all of their design but the type of materials or components and the type of mattress which is “best for you” is always a personal preference. There are also better quality and more durable versions and lower quality and less durable versions of most foam materials so regardless of which type of foam or which type of mattress you tend to prefer based on testing different types of mattresses … the goal is always to make sure that you know the type and quality of all the materials inside it so that you can identify any weak links in the mattress and make more meaningful comparisons with other mattresses (see this article).
There is more about the most important parts of the “value” of a mattress purchase in post #13 here. Softness and firmness is very subjective and a mattress that feels too soft for one person may feel to firm for someone else. The “best” mattress for you (regardless of whether it is best for anyone else) is the one that is the best “match” for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences).
There is also more about the different ways to choose a mattress (online or local) and how to reduce the risks involved with each of them in post #2 here.
Yes … I would avoid the major brands or any mattress where you aren’t able to find out the type and quality of the materials inside it (see the guidelines here).
When you are considering an online choice the one of the most important parts of your purchase will be a more detailed conversation with the manufacturer or retailer so they can help “talk you through” the options that are best for you based on the information you provide them, your local testing on similar mattresses, and on the “averages” of their customers that are similar to you.
These are different mattresses so the first step is to decide which of these you are most likely to sleep well on (which is the most important part of the “value” of a mattress purchase).
The Aria is similar to the Tempurpedic Cloud Supreme, the Colonial is similar to the Tempurpedic Cloud Luxe, and the Dreamfoam 13" gel memory foam is also similar to the Tempurpedic Cloud Luxe so I would test the equivalent Tempurpedic mattresses locally to see which one is the best match for you in terms of PPP which will help you narrow down your choices.
Once you have narrowed down your choices and have talked with each of them on the phone … then you can also compare them based on the type and quality of the materials inside them (especially in the upper layers which are the weakest link of a mattress in terms of durability) and on all the other parts of your personal value equation that are most important to you (including the price and the options you have available after a purchase if your choice doesn’t turn out as well as you hoped for).
You can see my thoughts about buying from Costco in post #4 here. They certainly wouldn’t be the best source of guidance and most of their mattresses tend to use lower quality materials than I would be comfortable with and they aren’t generally the best quality/value choice either but if you decide on one of their better quality mattresses then at least they have a good return policy (although other online sources that may have better quality/value mattresses and offer better guidance may also have very good return policies as well).
The “value” of a mattress purchase depends on a combination of which mattress is the best match for you in terms of PPP, the quality and durability of the materials inside it, and all the other criteria that are most important to you, but if you are committed to a memory foam mattress then the mattress shopping tutorial includes a list of the better online sources for memory foam mattresses I’m aware of which includes Novosbed and Dreamfoam (which is also a member of this site). If you do decide on Dreamfoam I would also make sure that you purchase from the Dreamfoam site rather than Amazon so that you have the benefit of the 10% discount they are offering (see their facebook page here) and their 45 day comfort guarantee.
You can read more about Amerisleep and their sister companies and their so called “expert sites” that pose as being independent in post #2 here and the posts it links to. A forum search on Amerisleep (you can just click the link) will bring up more about them as well. While they are in a “better than average” value range compared to most mainstream choices … there are also other options available to you that for most people would be a better quality/value choice.
As you mentioned in your earlier comments (which I would agree with as you can see in the guidelines I linked earlier) … I would avoid the major brands completely because they tend to use lower quality less durable materials in their comfort layers than I would be comfortable with in their price range (which means the sale price not the fake regular price) and they are one of the most frequent sources of buyers remorse much too quickly after a purchase.
If you let me know your city or zip code I’d also be happy to let you know about any of the better local options or possibilities I’m aware of as well.
Phoenix