Hi Bhutanim,
The first place to start any research on mattresses is the tutorial post here which has all the basic information, steps, and guidelines that can help you make the best possible choices.
A mattress is only as good as it’s construction and the quality of the materials inside it regardless of the manufacturer but unfortunately Stearns & Foster doesn’t provide the information that an educated consumer would need to make an informed choice. Most of the major manufacturers use lower quality materials in the comfort layers than many smaller manufacturers which is the reason that a mattress loses its comfort and support or develops impressions much more quickly than they should. As you can see here … the Kathryn has over 6.5" of foam and some synthetic fiber over the innersprings and the fiber and at least 2" of the foam (the hypersoft and ultrasoft) are lower quality materials that would be subject to more rapid foam softening and breakdown or impressions than higher density foams or materials. Some of the other layers may be lower quality as well and the lower quality/density foam in the comfort layers would definitely be a “weak link” in this mattress. In general I would avoid all major manufacturers because of their use of lower quality materials and their relatively poor value and the much higher risk involved in buying any mattress where the manufacturer doesn’t disclose the quality of the materials they use. I would always avoid any mattress that had more than about an inch or so of materials that were either unknown or lower density/quality and once you are at about 2" or more I would consider the purchase to be risky.
You can read a detailed analysis of Saatva mattress in this thread and a forum search on Saatva (you can just click this) will bring up more posts and feedback about them as well. To their credit they disclose the details of all the materials in their mattress and while outside of your own personal testing or sleeping experience there is no way to know with any certainty how good a match they may be for your specific needs and preferences in terms of PPP … I would certainly choose the Saatva in terms of durability and value. Even if they are not a good match for you … they have a very good return policy so the risk of an online purchase that you can’t test ahead of time is reduced.
I would also tend to be very cautious about using reviews as a replacement for actual mattress research and they are also a very risky way to choose a mattress (see post #13 here).
Phoenix