Hi peteza,
There is a list of some of the better online options I’m aware of that are members of the site in post #21 here (including all of the manufacturers you mentioned) that are among the better options I’m aware of and many of them make customizable latex mattresses with individual layers or components that can be exchanged. A few others are also in [url=https://forum.mattressunderground.com/t/manufacturers-do-it-yourself-online]post #3 here[/url]. I don’t know the length or details of each of their return policies or the options they each have available off the top of my head but you could check their websites to quickly find out. They each make different designs and have different features that include customizable or exchangeable comfort layers, support layers, or both as well as offering different types of latex in their mattresses. Post #6 here has more information about the relative “quality” of different types of latex. They all have more details on their site.
There are of course others as well of the same general type (too many to look for and list and I don’t have a database that I can search by specific criteria other than the forum lists) but if you are looking at any others and would like some thoughts or feedback about them then I’d be happy to make some comments about them. A forum search with the name of the manufacturer will usually bring up more information about any others as well.
Phoenix