Hi jacoro1,
Welcome to the Mattress Forum! 
You’re very welcome, and I’m happy that you’ve found us.
Your question about thickness is a good one, but the thickness of a mattress is just a side effect of the design and by itself isn’t particularly meaningful because whether a thicker or thinner mattress would be better or worse for any particular person will depend on the specifics of the materials (type, firmness, etc.) and on all the other layers in the mattress. Thickness is only one of many specs that are used to make different mattresses that perform and feel differently and that makes a mattress suitable for one person and not another. There is more about the effect of thickness in post #14 here. Regardless of how thick or thin a mattress may be, the most important part of the “value” of a mattress is how suitable it is “as a whole” for your particular body type, sleeping positions, and preferences in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) regardless of how thick it may be.
The main benefit of a thicker latex mattress is that it can be more adaptable for heavier weights and multiple sleeping positions. It will compress from softer to firmer more gradually which means that there is more “range” of compression without the mattress becoming too firm for heavier weights (or parts of the body). A thicker mattress can also be part of a specific design that requires it such as some types of zoning or layering that needs more layers to accomplish the design goal of the mattress. It can even just be a matter of preference rather than “need”.
In the large majority of cases, 8" - 9" of latex is easily enough to include the combination softer layers (or sometimes sections) for pressure relief and firmer layers for support that most people of average or even higher weights would need. In some cases, people that have higher body weights or larger body types may choose more than the “average” thickness and may prefer the feel and extra adaptability of say 12" of latex. Thicker mattresses can also use firmer materials because thickness and softness are very related and work together.
These are all good questions to ask the manufacturer or retailer of a mattress so they can discuss the differences between the different options they have available in terms that are more specific to the layers they use or options they provide. They will know about the differences in the products they offer and based upon the information you provide them in a phone conversation and their experience with similar somatotypes and sleeping postures they can best recommend a configuration using their componentry that they think will suit your particular needs. And one of the nice things with a component-style system is the ability to customize your comfort over time but rearranging and even switching out particular layers.
Post #2 here has some generic guidelines for different body types and sleeping positions, the first part of post #2 here also has more information about couples that have a larger weight differential and post #14 here has more about the benefits of thicker comfort layers and thicker mattresses.
Regarding your choice of materials, latex is certainly quite durable and can work well with various weight ranges and sleeping styles. Without getting you back down into the “rabbit hole”, there is a post here that consolidates and describes the differences between the two styles of latex, Dunlop and Talalay, and the different blends that you may find as a useful reference.
The brands you mentioned do offer good latex options, and SleepEZ and Foam Sweet Foam are members of this site which means that I think very highly of them and that I believe that they compete well with the best in the industry in terms of their quality, value, service, knowledge, and transparency. They are extremely knowledgeable about latex and different configurations, and I would not hesitate to recommend them for your consideration. You may also wish to take a look at other site members here, many which offer very good values on latex mattresses.
Overall, the steps involved in choosing a mattress are outlined here and you may find these useful as well.
Phoenix