Hi buttercupbetty,
Only you can decide whether a layer feels soft or firm because softness and firmness is subjective and what feels soft for one person can feel firm to another. Based on the ILD range though (listed in the previous link) it’s more in the medium range than soft.
When you are building your own mattress then only your own experience can answer these types of questions and give you the reference points and personal experience you need to build your own mattress. This is part of the challenge of the approach you are taking. Each person can be very different and without personally testing different ILD’s and different types of latex so you have good reference points then you are mostly looking at trial and error and “best guesses” as far as what works best for you. As I mentioned previously 75D Dunlop is a little firmer than many people would be comfortable with in a comfort layer although increasing the thickness of the comfort layers (by adding another layer) will make it a little softer. Given your feedback I would probably be going with something softer than 75D.
The link Karl sent you doesn’t include any information about ILD and it only lists three of the densities that Latex Green makes (they are all listed in the previous link I posted). He may not carry all of them.
It’s not in a single post but in the progression of the thread. I would start reading from post #9 onwards although the earlier posts will give you some insight and context into the options he was also considering and used as a reference point. He started off with his 6" support layer (two 3" layers) and slept on it and then used his sleeping experience on this single layer to guess at the thickness and softness he needed in the comfort layer rather than buying all the layers together. I would make sure that you don’t use his choices (or anyone else"s) as a basis for yours though because each person is very different and someone else’s experience may be very different from your own but I wanted to give an example of an overall approach to a DIY design.
He didn’t mention the cover he ended up using but it was the last step of the process. If I was adding a wool topper then I would choose that after the cover … bottom to top and each step based on your “best guess” and your actual sleeping experience on the step before it. You may still make mistakes and end up with layers that need to be exchanged or that may not “fit” in your overall design (or that need extra layers to be added that you didn’t expect) but that’s part of the challenge and learning process involved in any DIY project.
The guidelines I would use are in post #8 here about choosing a topper. Post #2 here also has some links to some of the pages that include some of the theory behind layering and matching different body types and sleeping positions but these are just generic concepts and each person is different. It’s only possible to know with any certainty based on your own personal experience in either testing different mattresses with different designs (where you know the specifics of what is in them) that you can use as a reference point or through your own sleeping experience and some trial and error.
Post #2 here (around the Seattle region) and post #2 here (Kitsap peninsula) may give you some places where you can do some local testing to help you decide on the combination that may work best for you.
Phoenix