Hi blasky,
Welcome to the Mattress Forum! 
The purpose of this forum is not to tell you what mattress to buy, or inform people of what mattress I might buy (this would have no bearing whatsoever on what you should choose), but instead help provide you the tools so that you can analyze and select a mattress on your own. It’s not possible to make specific suggestions or recommendations for either a mattress, manufacturers/retailers, or combinations of materials or components because the first “rule” of mattress shopping is to always remember that you are the only one that can feel what you feel on a mattress and there are too many unknowns, variables, and personal preferences involved that are unique to each person to use a formula or for anyone to be able to predict or make a specific suggestion or recommendation about which mattress or combination of materials and components or which type of mattress would be the best “match” for you in terms of “comfort”, firmness, or PPP (Posture and alignment, Pressure relief, and your own Personal preferences) or how a mattress will “feel” to you or compare to another mattress based on specs (either yours or a mattress), sleeping positions, health conditions, or “theory at a distance” that can possibly be more reliable than your own careful testing (hopefully using the testing guidelines in step 4 of the tutorial) or your own personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
In this situation you would need to find out the information listed here so you can compare the quality of the materials and components to the durability guidelines here to make sure there are no lower quality materials or weak links in a mattress that would be a cause for concern relative to the durability and useful life of a mattress before making any purchase. Unfortunately, Costco doesn’t provide that information on their web site, but if you’re able to procure that for the Novaform Firm and post it back here I’ll be happy to comment upon it.
Regarding the Tempurpedic, while they do tend to use better quality materials in their mattresses, they don’t tend to share that information much publicly. You’d again want to be provided the details of the layers within the mattress before making a decision on this or any other product.
When selecting a mattress, the first place to start your research is the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice … and perhaps more importantly know how and why to avoid the worst ones.
Two of the most important links in the tutorial that I would especially make sure you’ve read are post #2 here which has more about the different ways to choose a suitable mattress (either locally or online) that is the best “match” for you in terms of “comfort”, firmness, and PPP (Posture and alignment, Pressure relief, and your own Personal preferences) that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for and post #13 here which has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on all the parts of your personal value equation that are most important to you (including the price of course and the options you have available after a purchase if your choice doesn’t turn out as well as you hoped for).
As for “value”, while price is certainly important of course, the “value” of a mattress purchase is what is most important and price is just one of many factors that can affect the “value” of a mattress purchase. There isn’t a “formula” that can be used to assess or “calculate” the value of a mattress because there are so many different variables and criteria involved that can affect the price of a mattress that can each be more or less important to some people and not to others who may have completely different criteria or definitions of “value”. The value of a mattress purchase is also relative to how a mattress compares to the other finalists you are considering or to other mattresses that are available to you in your area (or online if you are also considering online options). There are many reasons that a mattress that may be “good value” for one person or in one area of the country may not be good value for someone else that has very different needs and preferences or that lives in a different area.
There is more about the 3 most important parts of the “value” of a mattress purchase in post #13 here which can help you make more meaningful quality/value comparisons between mattresses in terms of suitability (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on suitability, durability, and all the other parts of your personal value equation that are most important to you (including the price of course and the options you have available after a purchase if your choice doesn’t turn out as well as you hoped for).
But overall, the first thing I would recommend before making any purchase decision is to find out the specifications (densities) of the foams in all of the mattresses you’re considering. If you’re not able to procure that information, I would consider purchasing any such an item a more “risky” choice.
If you are looking for other quality memory foam options, while not a complete list, there are some quality memory foam manufacturers in the site members listed here, all of which I consider to be among the best in the industry in terms of their quality, value, service, knowledge, and transparency.
I hope that’s helpful.
Phoenix