Hi ersendil,
The “official” membership list is a side effect of me getting to know people and them getting to know me. There are many manufacturers who will be added over time (there are a number who will be added over the next few weeks) and many others who certainly fit the profile that would qualify them to be members and these will be added over the course of time as our conversations go in that direction and they express an interest in the goals and values of the site.
Thanks for sharing your thoughts and insights and the reasons you chose to buy from them. You certainly made a good choice IMO and as you know I think highly of European Sleepworks and the Berkeley Ergonomics mattresses. (NOTE: European Sleepworks are now making their own mattress in a range of similar designs)
The reasons you outlined will hopefully be helpful to other members of the site who are considering them although I wasn’t aware that there were posts on the forum that indicated that split layers weren’t available on many of their mattresses because of course they are. I must have missed them.
If you mean a platform bed with slats (that don’t require a foundation) there are many of these and a few of them that are listed in the foundation thread here may be of interest (although bedframes and furniture aren’t something that I spend a lot of time researching since mattresses take up most of my available time :))
It may also be worth talking with another of the Berkeley Ergonomics retailers Scott Jordan who make and sell bedframes (although I don’t know if they ship them out of the area). NOTE ADDED: They are now a member of this site as well
Thanks again for a very informative post and most of all … congratulations on your new mattress 
Phoenix