Hi Mousehouse,
All of these models use a 6" base of latex (with two 3" layers that can be chosen separately) so the real difference between them is in the thickness of the comfort layer which can be either 2" or 3". The "special" also has an unquilted cover while the 9000 and the 10000 has a cover quilted with wool which will also affect the feel and performance characteristics of the mattress (they also have the option of using the unquilted cover).
The choice between these depends on a lot of interacting factors but in general it depends on height/weight/and body shape considerations and also on sleeping positions. In general ... stomach and side sleeping needs thinner comfort layers because they are "flatter" and side sleeping can use thicker comfort layers because it has more pressure points. The closer to the firmer support layers you are the more you will feel the support layer. Changing the firmness level of the support layers can also affect the choice of which comfort layer may work best. All of this is part of the many complex factors that are involved in a layer thickness choices and mattress design.
There's a lot more information and some general guidelines about how height weight and body shape can affect your
choices here
and about
different sleeping positions here
. The choices are also affected by how the different layers can be put together and interact and there's more information about this in the
overview here
and in the more detailed pages in the same section.
Your lighter weight increases the odds that a 2" comfort layer may be suitable but this would also depend on your sleeping position and on the firmness of the layer below it (you will be closer to the core and feel more of its characteristics with a thinner comfort layer). A non quilted elastic cover will also put you closer to the latex and you would feel it's properties more and it will conform a little better but you would lose the benefits of having wool in the quilting.
Outside of the general guidelines though that are based more on "averages" ... it's usually much better to talk directly to the manufacturer about which choice may work best for your specific and unique needs and preferences. They know all the fine details of every component and choice available in their mattresses and how they interact with different body types and sleeping styles and also have a large database of customers that would be similar to you which can act as a guideline. Some local testing on mattresses that use similar layers or materials can also help them to help you even better (so they can know where you may be different from the "averages")
Shawn or Jeremy are very good at going through your options with you and making sure that your choice is the best one possible. The more you have developed a sense of the general types of layering you prefer from local testing ... the more accurate they can be with their guidance.
Phoenix