Hi pattycake,
How “supportive” a mattress may be and the durability of a mattress are completely separate issues. Lower gauge coils are certainly thicker and firmer that the same type of coils that are a higher gauge (especially if they are linked coils rather than pocket coils) but the gauge of an innerspring is only one of many variables that determines the feel and performance and the quality and durability of an innerspring and the weakest link of a mattress in terms of durability is generally in the comfort layers not in the innerspring itself.
I certainly wouldn’t recommend purchasing a mattress where you don’t know the type and quality/durability of the materials inside it.
“Support” is often misunderstood because the goal of a “supportive” mattress is to keep the spine and joints in good alignment and this requires the type of contouring support that allows some parts of the body to sink in more (softer) and some parts of the body to sink in less (firmer) and this will vary on an individual basis. There is more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support/alignment” and “comfort/pressure relief” and “feel” and how they interact together.
Phoenix
PS: I switched our conversation into a new topic of its own because we were hijacking the original topic we were posting in.