Hi Bellawaves,
Welcome to the Mattress Forum! 
This would be a density of at least 85 kg/m3 (approximately 5.3 pcf), but as densities are within ranges, with those specifications you’ll probably want to look for something in the 85-90-95 kg/m3 range, with the 90 kg/m3 (5.6 pcf) being commonly classified as “extra firm” and the 95 kg/m3 (5.9 pcf) commonly being termed as “extra extra firm”.
That would be a good distance between the slats, as you’ll want to be 3" or less, with good center reinforcement to prevent slat bowing, for a latex mattress, even a thinner mattress like you’re considering.
Yes, you’re correct, unless the materials were the same as what you are considering here, the feel won’t be representative of what you’re looking to create.
Dunlop latex is most commonly poured in 6" cores, with some being poured in 3" cores. I’m not personally aware of anyone pouring in a 4" core. The “crumbling” that occurs with latex tends to be over quite a period of time from a combination of oxidation, UV and mechanical stresses, usually long after the useful life of the foam. With a proper cover as you’re considering, I personally wouldn’t have a concern with the abrasive forces creating a considerable “crumbling”.
Wool, when used in sufficient quantities, can be used as a method to pass 16 CFR Part 1632 and 1633, but any encasement purchased separately won’t carry that guarantee of certification because the manufacturer wouldn’t know what foams might be placed inside of their encasement, so wouldn’t have specific burn tests to certify it as such. The wool will be a very good product for temperature and moisture regulation, as you mentioned.
As for suppliers, a really good place to start would be the component list here. There’s quite a few latex foam suppliers and mattress cover suppliers as well, many who are members here of the site and quite knowledgeable about latex. That should give you a good start in your quest to change to a different style of sleep system.
Phoenix