Hi snoozer,
Like dn … I think if you’ve done some careful testing on combinations that are very close to what you are considering that you can use as a reference point (layer thicknesses, layer ILD, type of latex, type of cover) then the odds are much better that what you purchase will work for you. If the type and quality of the material is the same … then the main “risk” is the effect of any differences between what you tested and what you purchase.
As you mentioned the cover can also make a difference in how the mattress feels and performs.
You can also read a little more in this thread about how a separate topper can affect the feel of a mattress vs having the same layer inside the mattress cover.
It may also be worth considering first buying the mattress to see how well it works for you without a topper and then adding the topper as a separate purchase if it’s necessary.
You’re certainly talking with a very knowledgeable and experienced manufacturer and as you know I think highly of Arizona Premium.
Phoenix