Hi mantis,
Just in case you haven’t read it yet … the tutorial post here has all the basic information, steps, and guidelines you will need to make the best possible mattress choice … and know how and why to avoid the worst ones. It also has the information you need to be able to evaluate any mattress you are considering and make meaningful comparisons with other mattresses.
You can see some comments about The Mattress Expert in post #11 here and post #2 here and a forum search on themattressexpert (you can just click this) will bring up more information and feedback about them as well.
The most important part of any mattress purchase is making sure that a mattress is a good match for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences). If you are buying a mattress locally then careful and objective testing is the best way to know whether a mattress is a good match for you. If you are making an online purchase that you can’t test in person then more detailed conversations with a manufacturer or retailer and the information you provide them (along with the results of any local testing you have done) can help them to help you make the best possible choice based on the “averages” of other people that may be similar to you (see mattress firmness/comfort levels in post #2 here). With an online purchase … making sure you know the specifics and costs involved for a return or exchange policy may also be an important part of your personal value equation in case the mattress you choose doesn’t work out as well as you hoped when you sleep on it in “real life”.
Outside of how well a mattress matches your specific needs and preferences … the most important part of a mattress purchase is making sure you know the quality of all the materials inside it (see this article). Without this information there is no way to determine if the mattress has any weak links or make meaningful comparisons with other mattresses and you would be making a “blind” purchase.
A two sided mattress would be more durable than the same mattress that only has comfort layers on one side of the mattress. There is more about the pros and cons of a two sided mattress in post #3 here. While they are not generally available in the mainstream market … they are still commonly made by many of the smaller manufacturers across the country.
There is also more about choosing a mattress for those who are in higher weight ranges in post #3 here and the posts it links to.
This is certainly true in the mainstream industry and most of the major manufacturers but the good news is that there are many smaller manufacturers and better sleep shops around the country that will educate and inform their customers more than try to sell them anything they can convince them to buy and make higher quality and better value mattresses that are sold at fair prices every day of the year (see post #12 here).
If you follow the steps in the tutorial post one at a time you will have the highest possible odds of finding your “perfect” mattress
Phoenix