Hi NatalieC,
Welcome to the Mattress Forum! … you are a long ways away from most of the members here 
While I don’t have the depth of knowledge of the Australian market that I would for North America … I may be able to help in more generic ways.
Just in case you haven’t read it already … the information in post #1 here would be just as relevant in Australia as it is here and has some of the basic information, steps, and guidelines that you will find most helpful.
Post #2 here has links to some of the pages on the site that can help give you some insights into different types of designs and layering as it applies to different body types and sleeping styles.
Post #2 here includes some links to some of the better Australian threads on the forum and a link to many local or independent manufacturers around the country with some comments about some of them. Some of these would likely make two sided mattresses (they are much more common with smaller manufacturers than they are with the mainstream manufacturers).
A double sided mattress would certainly help even out the wear for anyone that was higher weight (you could both flip and turn it) and would be a good idea to increase durability. It may not help as much though with your different needs and preferences and the first part of post #2 here may also be helpful with some ideas about how you can accommodate different needs and preferences on the same mattress. with all of these posts I wouldn’t “study” or “analyze” the information as much as use it to give you a sense of possibilities that need to be verified with your own testing.
The mattress you listed is missing some specs that are important in order to make any assessment of it in terms of the quality of the materials and the specs are also very different in Australia than they are in North America so once you have them I will need to translate them in order to make any sense out of them.
What you need is the materials and components from the top down with the thickness of each layer and the density of any polyfoam or memory foam and the type and blend of any latex.
If I am understanding the specs correctly so far we have (top to bottom on one side) …
- Luxury damask knit cover This is a woven fabric and they don’t mention the type of fabric used.
Quilted to 48mm 25/60 Super Soft: This is almost 2" of quilting polyfoam (1.9") and since it is a little on the thick side (more than @ an inch or so) then the density of the quilting polyfoam would be important which appears to be 1.56 lbs which is reasonable for a two sided mattress depending on the thickness of the layers below it.
2 x infinity comfort layers (type or material, thickness, and density information is missing)
2 x HD Comfort layers (this is polyfoam but the thickness and the density information is missing)
Foam Box Surround Edge to Edge Security: This is the polyfoam edge support around the innerspring and the density information is missing
2 X Heavy Duty Needle Felt Pad: This is the insulator pad to even out the support of the springs and protect the foam from compressing into them.
Full spring Count of 256 Springs Per Square Meter: If I’ve done the conversion correctly then this would be 792 coil count (queen size) which would be good but 9 zone is a bit of overkill IMO and I wouldn’t pay any “extra” for it.
I will also need to find a conversion to wire gauge for the innerspring diameter in mm to make sense to me and while an innerspring is not normally the weak link of a mattress, with higher weights and a pocket coil that flexes independently I would want to make sure that the gauge was appropriate for higher weights.
So there are a lot of pieces of information missing that would be necessary to make a meaningful assessment of the mattress. Once you have this then it’s possible to assess the quality or relative durability of the mattress and you can also compare it to other similar mattresses that are available to you locally to make value comparisons.
Phoenix