Hi stenstageous,
First of all … thank you for your kind words. It means a great deal to me when the site can help people make better choices.
As you probably know … you are choosing between some great choices and have narrowed down your final options to choices that are all high quality and good value. although you already have some great options available to you … post #12 here has a few other memory foam options that you may want to consider if you want to make your final choices even more difficult 
At this stage it can become difficult to choose between choices that are all good quality and value but the best advice I could provide would be to make sure you have a longer conversation on the phone with each one of them. You may find that you “connect” with the information provided by one of them more than the others because the design or materials seem to be more suitable in terms of what is most important to you or they may somehow “connect” more with your specific criteria and this more detailed information or the insights they provide may not be obvious from research on their websites.
Secondly … I would include all the factors in your personal value equation that are important to you in your decision including of course the design and materials of your mattress but also some of the other factors that may be just as important to you or your “comfort” with an online purchase including the guidance, options, and benefits that come with the mattress before, during, and after the sale. The “value” that is added by things such as return or exchange possibilities, delivery method or costs, or other additional benefits that come with every mattress purchase or even just the knowledge and experience of each manufacturer in helping people in your particular circumstances and the confidence they inspire in you can be an important part of how comfortable you are in ordering from a particular online manufacturer.
All the objective, subjective, and intangible factors that are an important part of any mattress purchase can play a role in which of your final choices is best for you.
The good news is that all of them are head and shoulders above the choices that are typically made by the vast majority of consumers who end up buying a major brand from a chain store
I’m looking forward to hearing about your final choice.
Phoenix