Hi Gvm,
You certainly aren’t in a weight range where you will “need” 12" of latex vs 8" - 9" although it may be a preference if you were testing two mattresses in person and the difference between them was enough to justify the extra cost. There is more in post #14 here about the difference between thinner and thicker mattresses (and layers). When you can’t test a mattress in person before you buy it (or a local mattress that is a very similar design) then the best way to make a choice would be based on more detailed conversations with each manufacturer you are considering who can tell you the pros and cons of each of the options they have available (see mattress firmness/comfort levels in post #2 here).
Assuming that you are making apples to apples comparisons with the same type and thickness of latex in each one … the main differences between them is that Arizona Premium would be a lower cost and SleepEz has more individual layers which gives you more options to customize the mattress either before or after a purchase and there are differences in their exchange policies as well.
They are both great quality and value and when you are down to final choices between “good and good” then which one would be best for you would depend on your conversations with each of them and all the objective, subjective, and intangible parts of your personal value equation that are most important to you.
Phoenix