Hi goitsme48,
You’ve tried quite a list of mattresses 
All mattresses have 2 main functions which is to relieve pressure and to keep your spine and joints in good “neutral” alignment in all your sleeping positions. Both of these can be achieved with different designs using any type of mattress material. In other words all the information that you may hear about this material being better for back pain than that material is just marketing. The mattresses that are best for YOUR back pain are the ones that have a design that keeps your spine in neutral alignment in all your sleeping positions regardless of the materials that are in them.
I think one of the down sides with ordering online from retailers such as Costco is that they have little knowledge about the products they sell and you are limited to the luck of the draw in terms of finding out information that may help you make a suitable choice. They are just not what I call “mattress people”. In many cases they also don’t list their mattresses correctly or provide inaccurate information. Of course this can be offset to some degree by good return policies but each time you return a mattress you are starting all over again.
The Novosbed you tried is at least good quality but as you are mentioning it can sometimes be difficult to make a choice that fits your body type, sleeping positions, and preferences with an online purchase unless they have designed and/or tested their mattress to compare with more widely available mattresses in either material quality and layering and/or feel. A mattress that uses the same type and quality of materials and design doesn’t always perform and feel the same as another mattress that uses the same design and foam quality because even equivalent quality foams can have a different “feel” and performance.
I’m assuming you mean the Sleep Science ARA here? (the link was to the Aria from Novosbed).
I have seen several mattress listings in some of the Big Box stores that were listed or described incorrectly so I thought I would see if the mattress description matched the shipping weight. It doesn’t. 6.625" of 5 lb memory foam in king size would weigh 116.6 lbs. The mattress is listed as weighing 138 lbs. This means that the other components would weigh 21.4 lbs. If this is the case … then the remaining 6.25" of foam (22 cubic feet) would have to weigh 21.4 lbs less the weight of the cover. If this is the case then the base foam would be under 1.0 lb density which is clearly not possible. If the memory foam was only 4 lbs … then the density of the base foam would work out to about 2.0 lbs which is much more likely. Either their specs are wrong or the shipping weight is wrong.
In addition to this … Sleep Science uses Chinese foam that isn’t CertiPur certified and doesn’t seem interested at all in providing any information about how their foam has been tested (see post #8 here). For this reason along I would avoid them or any mattresses that used Chinese or Asian memory foam that has no certification.
As you probably know Brooklyn Bedding (who makes the Dreamfoam mattresses) is a member of this site which means that I consider them to be among the best quality/value in the country.
The choice between memory foam (slow recovery) and latex (fast recovery) is really a matter of personal preference because they have a very different “feel” and performance to them. Once you have made this choice (and local testing on several examples of both materials will give you a good idea of which you prefer) … then you can exclude the other one.
You may also want to include the mattresses they have now started to list on their own site as an option. All of these have exchangeable layers in case you want to exchange your choice for a different firmness level or even a different material and one of them (the Camilla) has a lower cost than the Eurotop on Amazon.
The two best ways to “fit” a mattress to your own needs and preferences are either local testing (for an actual mattress purchase or as an approximation or guideline for an online purchase) or talking with an experienced and knowledgeable retailer for an online purchase who can help you choose their model or layering that best fits the “averages” of their customers based on body type, sleeping positions, and preferences … although of course each person may not be “average” or fit inside the averages of other people.
While I can’t help anyone with which mattress to choose, I can certainly help eliminate the worst choices, help link the members here to more knowledgeable people, help them identify what information is accurate and what isn’t, point to any warning signs I see, and help them identify which parts of a mattress purchase is most important to them and how to decide on their own “personal value equation”.
Personal testing, more detailed conversations with knowledgeable manufacturers and retailers, and meaningful comparisons based on knowing the materials in a mattress and on the services and options provided by each manufacturer or retailer are the best way to make the most suitable choices once all your options are good ones. In the end only you can decide which one has the best value by your definition of “value” based on all the objective, subjective, and intangible factors that are involved with any mattress purchase.
Some of the better options and possibilities I’m aware of in the Minneapolis / St Paul area are listed in post #2 here.
Hope this helps
Phoenix