Hi on_the_edge.
Welcome to our Mattress Forum. 
Latex and latex hybrid would certainly meet most of your criteria for something durable and easy to move in and out of the van, plus your tendency to sleep hot. I’m personally not a fan of visco-elastic memory foams in vans because of the wide swings in temperature and humidity, their tendency to form mildew and host dust mites and also because of the change firmness with increased temperature and pressure.
Memory foam does a very good job at minimizing motion transfer, but it generally is the least breathable and most insulating of the foam comfort materials, so the temperature can be an issue especially for those that have the tendency of sleeping hot. If you do choose memory foam you’d want to make sure that you don’t choose something with so much memory foam on top that you sink in too deeply.
Although I do personally like the feel and properties of latex, the choice of materials is a personal preference and there are many people that prefer a Memory Foam feel and are “used” to it to such a degree that any change to a different material may be perceived as very uncomfortable. There is absolutely nothing wrong with using Memory Foam in a mattress… provided that it meets durability guidelines here .
Your comfort choice of firm or medium-firm is appropriate for your stomach sleeping. For your stomach sleeping position, you may wish to review the guidelines in this [url=Your sleeping style, preferences, and statistics - Your sleep positions - The Mattress Underground] Sleep Positions Article [url] so that you avoid hyperextension in a swayback position that can cause back issues.
Latex in general is also the most breathable and “temperature neutral” of all the different types of foam materials and it is a great choice for all temperatures and climates but the firmness of a mattress and how much you sink into it can also affect sleeping temperature as well. It is also important to keep in mind that the layers that are closer to the top sleeping surface (comfort layers) will have the greatest impact upon comfort and sleeping temperature (including any mattress pad, sheets, and linen).
I am not sure if you came across some of our posts that discuss temperature regulations issues, but you can read more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 here more about tracking mattress temperature regulation issues potential causes ~ Post #2 here (at least to the degree possible for a specific mattress) and the posts it links to that may be helpful. You may also be interested in the information in post #29 about temperature regulation and mattress microclimate.
Some options you may be interested in considering are…
Sleep EZ’s 9" Latex RV Mattress, Full Size - $525
Latex Mattress Factory’s 9" Luxerion Latex RV Mattress, Full Size - $595
Or you could talk to Ken Hightower at Arizona Premium about his thoughts on the 6" Dunlop base + 2" Talalay topper for an 8" latex mattress coming in at around $515
You mentioned that both you and your girlfriend are “combo sleepers.” With combination sleeping it is usually wise to choose a comfort layer that is a little thinner than your “deepest” sleeping position would normally require (typically side sleeping). Most side sleepers will fall in the range of needing roughly 2" - 4" in their comfort layer, where a stomach sleeper may only need 1". Depending on your BMI you’d probably do well with 1" to 3" of foam for your comfort layer.
Regardless of which mattress you may ultimately choose, it’s important that you have a detailed conversation with each vendor prior to your purchase. Our Trusted Members are knowledgeable and experienced online manufacturers that can help with making the best comfort/support choice if they are given your stats and information about your body types, sleeping styles, general preferences and history, some general information about mattresses you have tested and done well with, and any other specific information or circumstances that could affect your choice of a mattress.
I’d certainly follow up on your intention to “get a coconut coir mattress pad to assist with moisture management and potentially support between the slats” as an inappropriate foundation might void the warranty of the mattress. I’d make sure to check with the vendor if the slatted modular wooden foundation you have in place is appropriate for your unit. A slatted platform bed is also perfectly suitable as long as the slats are spaced close enough together (again 3" or preferably less for latex) A coconut coir pad would be a good investment in this case for the added support it would afford the mattress.
You may also want to consider that a full mattress size measures 75" x 54" and this may be a bit problematic as your current setup accommodates only a 72" mattress length so you may need to ask for the layers to be cut to fit the space in the van.
Phoenix