Hi heyphoenix,
Good luck in your testing 
I actually think their exchange policy is very fair and reasonable. You can read about it in post #4 here.
12 years for a traditional innerspring/polyfoam mattress is well above average and is most likely because of the quality of the materials they use. The longevity of a mattress is also relative and has to do with the suitability of someone’s choice as much as the quality of the materials in the mattress itself because a mattress that works well for one person for only a year before they are outside of their comfort and support range (even though the materials are not worn out) may work well for someone else for ten years or longer. You can read more about the various factors involved in the durability of a mattress in post #4 here.
I didn’t see any other specific questions in your post so the only other general comment I would tend to make would be a suggestion to make sure you know the quality of all the materials in any of the mattresses you are considering so you can lessen your odds of being unhappy with your choice in a year or two down the road when it no longer feels or performs the way it did when it was new or when you tested it in a showroom. As you know this usually translates into avoiding major brands completely but each person may use very different criteria for their own personal value equation.
Only if you are in the Phoenix area and make an appointment to visit their factory although there may be similar designs available that you can test locally.
Some of your options are very good ones and some I personally wouldn’t consider at all.
Phoenix