Hi nej,
I would question whether this was the organic version of the Latex Green cores because the densities and ILD ranges they are posting don’t agree with the range of latex specs in their organic line (they are the specs and densities for the Latex Green 100% natural line).
Outside of dn’s great comments … if you are planning to build a DIY mattress (as opposed to a kit where you are buying a complete mattress with exchangeable layers) I would first read post #15 here and post #2 here so that you have realistic expectations of success and as dn mentioned what you learn along the way (with your testing and experimentation with different layering combinations) is just as important as any potential cost savings (which may not happen).
As dn also mentioned and I would echo … I would use a mattress design that you have tested in person or a successful design that is suggested by an online manufacturer based on “averages” and then duplicate it to the best of your ability using the same type and blend and ILD of latex in each layer and the same or a very similar cover.
The more familiar you are with different latex combinations in terms of PPP … the higher your odds of success.
Outside of a bed rug which would be a big improvement compared to the floor … there are several DIY foundations (two foundations and a platform bed) with detailed instructions and a materials list that are linked in the foundation post here that were quite inexpensive to build.
Phoenix