Hey D,
A couple of thoughts here. Can I assume you are less interested in keeping the mattress “natural”? I make the observation as you are using the polyfiber and foam in your panel/cover layer.
Having cleared that up, a couple of more thoughts.
I prefer a two-sided mattress, although mine is extremely firm on one side and just very firm on the other side, so my intentions are not to flip it, just rotate every 6 months. The old school mentality has me sticking with the idea that all things being equal, two sided is “better” than single. Of course, that is not true in all cases, but the belief “calms my mind” 
if you will.
Having said that, dual sided is an option for you, albeit not so necessary and more costly, as latex is a resilient material and should hold up a good long time, plus you are probably not gluing the layers together since you are leaving the option to interchange layers, so flipping would be a tough option.
I think you would be fine with the 4cm option, but I would consider the cover/panel options to follow.
“A mattress is only as good as it’s weakest layer” so you dont want to skimp on one layer and defeat the purpose of the entire project.
Looking at the single sided option, you have put together a “less is more” combination, which I think is the best way to approach this. Way too often you see many of the “national” brands stacking the mattresses with layers upon layers of potentially failing materials that render the mattress useless when any one of those layers fail. But, I must admit, they do look exquisite on the showroom floor.
If you want to keep it natural, perhaps a wool or cotton in the cover layer, as it breaths better and regulates/controls temperature better by dissipating heat better and wicking moisture away from your body.
As far as the base layer, most would say any quality dense/HD polyfoam 1.8lb layer between 1/2" to and 1" should be fine (also ok for adjustable bases so long as your pocketed coils do not have any stability rod around the perimeter, that might affect the adjustable base functionality).
You can use a higher density dunlop for that base if you want to keep it all natural, but that may kick the price up.
The other thing to consider, companies like SoL use all dunlop, so having dunlop as your comfort layer is certainly a good choice. Others prefer to use talalay for that upper comfort layer as the density is more consistent throughout the entire thickness of the layer. Ultimately, a 19ILD is a 19ILD, until you get past the first 25% of depression, then Dunlop will start to feel a bit denser than Talalay. Which could affect the shoulders and hips, if you should approach the 200lb+ weight ranges. Talalay, of course, is usually a bit more expensive.
I know I am jumping back and forth a bit, but I am just trying to think about it as if I were going to put this system together.
Another thing to think about that I touched on before is that cover, as it stands you are approaching an inch of “foam” in that layer. Most synthetic foams do break down faster than your latex will, which is why I like wool, cotton, horsehair (I just got a horsehair pillow and it is great) better in the cover panel, as you dont want that inch of cover, combined with the first inch of your upper comfort layer to bother your back if you begin to sink a bit. You dont want that 9/10 of an inch in the cover panel to be an part of a potential issue for you down the road, since you are building such nice system, the cost of wool or cotton in the cover panel may be worth it if you are able to manage the cost and cost average over the next 10-15 years or more of owning your new setup. You have taken the time to build yourself a nice system which should last you a long time, if you are able, spending a little more now, will save you in the long run. Good luck with your build. Hope it works out great! I know some of the other members will get deeper into the technical aspects of the materials, ILD’s and the like, but my goal was to put it in layman’s English, hoping that would make it easier to follow.
Norm