Hi zen4life,
Innersprings can be very “technical” and there are many things that affect how they perform. Things like coil count, number of turns, coil density, coil geometry, types of helicals (if any which are not used in pocket coils), methods of securing the coils, coil height, foam borders or “tubs” and many other factors all lead to the end result which can be measured by two questions which are “how well does this mattress relieve pressure?” and “how well does this mattress keep me in alignment in all my sleeping positions?”. Coil counting or using the gauge of coils alone as a measure of the durability or performance of a mattress can be very misleading. They are a piece of the puzzle but there are many others as well.
In addition to the types and specs of the coils themselves … the layers in between the coils and you will also have a big effect on the suitability and performance (and firmness and durability) of any particular coil unit and the mattress itself. To say for example that 13 gauge coils creates a more durable mattress than 15 gauge coils is not necessarily accurate unless all the other factors also support this. Even the amount of “working steel” in a mattress (or the weight of the innerspring) … while more accurate perhaps than other measures or specs … does not tell the whole story and these are specs that aren’t generally provided by the manufacturer. As a single example … coils that are joined by helicals are not as independent as pocket coils but they will also spread pressure between more coils and so can be more durable … at the cost of motion separation and the ability to conform as well to different body shapes. This would also be affected by the type and amount of materials over the coils. The equivalent in foam would be “point elasticity” which is the ability of small areas to compress without affecting the areas next to them.
There is more about the different types of innersprings in this article.
Both Quantum coils and Bolsa coils are pocket coils which act independently and are used in different combinations to help create the desired performance characteristics of a mattress within the budget restrictions of the design and target price. The Combi-zone uses these two types of coils together to create different response zones in different areas of the mattress. The heavier parts use the firmer coils while the lighter parts use the softer coils to give more “gentle response” in these areas. As you can see as well from the Combi-zone description … coil height is more of a money saving measure which can lead to the use of less (more expensive) foams to create similar mattress heights which consumers “translate” into higher quality. I also question the value of a seven zoned system which IMO is more about marketing than actual benefit.
Basing a decision on a mattress based on coil specs alone would be somewhat like saying that larger wheels on a car have less rolling resistance and so the car can go faster without taking the engine, type of rubber, gear ratios, car weight, or many other factors into account.
None of this is to say either that the Green Sleep is not a high quality mattress (which of course it is). They use a high quality innerspring which is very strong, add 3" Dunlop latex (65 is a density measure based on kg/cu. meter which is in the soft range of Dunlop and would typically be a range in the low 20’s or even high teens but would also be firmer than the equivalent ILD talalay because it gets firmer faster as you compress it more) and add thick layers of organic wool and organic cotton both of which are expensive materials in a mattress. The quality is undeniable … but the “value” is open to question. There are many other manufacturers that use similar materials that are in lower price ranges but of course each person’s personal value equation is also subjective and depends on the many parts of a mattress purchase that are most important to each person.
If this mattress “worked” for you then I’m not sure of the value of changing it. Did it actually “feel” too soft (in the sense that you were out of alignment) or is it more a matter of thinking that a combination of 13.75 gauge with 17 gauge would be “better” (regardless of what was used over the coils to create the actual firmness of the mattress rather than just the coils themselves).
These are the types of things that I would discuss with the manufacturer but personal experience … with the guidance of the manufacturer themselves … would always “trump” theory. As I mentioned … the upper layers are usually the “weak link” of a mattress. Thinner upper layers will bring the lower layers (such as an innerspring) more into play and may change what works best and is most durable (such as in mattresses where the coils themselves are a big part of pressure relief") but it is the balance and interaction between all the layers that results in the end product and creates the overall durability of the mattress.
Phoenix