Hi WyndRacer,
You can see some thoughts and feedback about Saatva in post #1 here and the rest of the topic and a forum search on Saatva (you can just click the link) will bring up more comments and feedback about them as well. In very general terms for most people it would be a “better than average” quality/value choice compared to most of the mainstream mattresses made by the major manufacturers but it wouldn’t be in the same “quality/value” range as many of the other options that most of the members here would know about as a result of the information on the site.
There are no specific ratings or “numbers” for edge support but most mattresses that have edge support will say so in the description although it won’t tell you “how firm” the edges will feel for you or how the edges compare to the rest of the sleeping surface.
Outside of PPP (Posture and alignment, Pressure relief, and Personal preferences) a mattress is only as good as its construction and the quality and durability of the materials inside it regardless of the name of the manufacturer on the label. The weakest link of a mattress is generally in the softer comfort layers on top of the springs and not the springs themselves but the major brands tend to use lower quality/density materials in the comfort layers which is the reason I would generally avoid them along with any mattress where you aren’t able to confirm the quality and durability of the materials in the mattress (see the guidelines here). Their springs are generally fine and aren’t a weak link in the mattress … it’s the rest of the materials that are on top of the springs that are usually the problem.
Phoenix