Hi ivo,
As you know … I believe your best chance of success when you are buying a new mattress is to follow the steps in the tutorial post one by one.
If you are looking for an online memory foam mattress then I would suggest using local mattresses as your testing grounds that are close approximations to the mattresses you are considering. Tempurpedic is the most common comparison because they are so widespread and most online retailers or manufacturers have a good sense of which of the Tempurpedic mattresses approximate their own mattresses in terms of PPP for most people. You can also check their websites or talk to them about other mattresses that may be available locally that may also be good reference points for testing. In some cases if you test a local mattress that works well for you and you have all the specific layer by layer details of what is inside it then this can also be very helpful as a guideline in your discussions about which of the options they have available may be the closest to what worked well in your testing. The more specific and detailed information you can provide them about you, your history, and the mattresses that you seem to do best with, the more you will help them to help you make the choice that has the highest chance of success. The tutorial post has a link to a list of some of the better online memory foam choices I’m aware of.
There is also more about the different ways that one mattress can “match” another one in post #9 here that may be helpful and you can use as a reference point in your conversations.
If you are still uncertain or don’t have much confidence about what may be “best” for you after local testing and talking with the online options you are considering then the return or exchange policy may also be an important part of your personal value equation to lower the risk in case the “best efforts” of both you and the retailer/manufacturer you are dealing with doesn’t turn out as well as both of you hoped.
There may also be some good options available to you locally that you can test in person and if you let me know your city or zip code I’d be happy to let you know of any of the better local options or possibilities I’m aware of.
Phoenix