Hi Bazinga,
You’re right and I didn’t see your post until after I had posted my reply. I could probably have saved lots of typing and just have posted the “short version” which would have been “try removing the 4” layer" 
Some people are very attracted to the softest possible mattress in spite of the risks that can be involved and seem to like the latex foundation because of the additional softness it provides and I’ve seen some people use it in combination with the softest PLB mattresses such as the Beautiful or the Worlds Best Bed which is softer yet. It would certainly be much more risky in terms of potential alignment and lower back issues for most body types and it would also be more risky in terms of roll together for a couple that wasn’t more “balanced” in their weight differences.
The better online sources for toppers and other mattress components I’m aware of are listed in post #4 here. If you are looking for an inch of Talalay then it would be worth considering either Mattresses.net or KTT who both sell 1" talalay layers at very good prices.
As you know Flobeds is one of the members of the site and I think very highly of them. They certainly have a unique design with their vZone that can be a very good option for those who have more challenging circumstances where finding a good “match” in terms of PPP is more difficult.
Phoenix