Hi BrissieMum,
Unfortunately I don’t have the time or resources to be able to do more detailed research into the Australian market (there is a long time to go before I would even be happy with the research in the North American market) but the same general guidelines that are linked in post #1 here would apply in any market. There is also no “formula” that can accurately predict which type and design of mattress would best match your body type, sleeping style, and preferences and local testing that focused specifically and more objectively on pressure relief and alignment is much more accurate than any “theory at a distance” although there are some general guidelines that are linked in the earlier post.
There are several topics in the forum that include quite a number of sources in Australia and some feedback and conversations with others from down under that would be well worth reading as well. They are in this topic and this topic and this topic and this topic and this topic and this topic. There is also a discussion in another forum here which may be useful as well. Post #7 in this thread also has a list of many Australian manufacturers with comments about some of them as well.
It seems to me that all of the mattresses you are mentioning are a little on the costly side but I’m not so familiar with pricing and the details of the Australian market so may not be as “educated” an opinion as it would be for North America. I think that the threads I linked would probably include some better “value” though.
Only you can really answer this because different people would have different answers depending on many variables but in general and “average” terms I would think it would be a “large” difference yes … perhaps not “huge” (I’m not sure how to “measure” either of them) and it would also depend on factors besides just the thickness of the layers. You can see some of the potential benefits of thicker mattresses in post #14 here.
I would have a hard time imagining that you couldn’t find latex or layers that were suitable in Australia (either Talalay or dunlop both of which come in a wide range of firmness levels) but this would certainly be an option (although I would imagine a very expensive one and the shipping and import charges may be more than the cost of the material itself). the type of layering you are mentioning with a 6" support layer (either Dunlop or Talalay) with two or three inches of softer latex on top (either Dunlop or Talalay) is perhaps the most common type of latex mattress construction (although there are also many people who sleep directly on a single latex core with perhaps a thin layer of softer latex or other quilting materials on each side).
This would depend entirely on the preferences of each person. Some will prefer “less springy or bouncy” and some wil prefer more. It would also depend a lot on the type and firmness of the layering, the specific design or the mattress, and on the other components (such as the ticking and quilting) in the mattress as well.
Generally the firmer layer would be on the bottom yes and not just for feel (the deeper layers generally have less effect on the “feel” of a mattress for most people but it would provide more stability and deep support). How it “felt” though would depend on the specifics of how all the layers interacted together (especially from the middle of the mattress and up) and with the specific body type, sleeping style, and perceptions of each person. Your own personal testing will answer “feel” and “individual performance” types of questions much more accurately than any “theory at a distance”. Besides this … the manufacturer themselves would be the next best source of this type of information because they are much more familiar with all the details of their mattresses than I am and would be in a much better position to be able to tell you how each mattress they make would “feel” (on average at least) for similar body types and sleeping styles.
Phoenix