Hi sugarfree,
You may not have read the tutorial as closely as you could have since I would normally suggest avoiding major brands such as Stears & Foster and the larger chain stores that focus on them (see the guidelines here).
The tutorial also links to some good information about the 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 all the parts of your personal value equation that are most important to you).
At the very least I would make sure that you found out all the information listed in this article so you can compare the quality and durability of the materials to the quality/durability guidelines here to make sure that there are no lower quality materials or weak links in the mattress that could have a significant effect on the durability and useful life of the mattress.
It may be worthwhile reconsidering your purchase if that’s still possible.
Phoenix