Hi Barnaby,
Congratulations on your new mattress. 
I was just scanning the thread and you’ve come a long way since you started testing mattresses and I think you worked with some excellent manufacturers and ended up making a great choice. It’s tough to go wrong when all the “worst” choices have been eliminated!
I also think that Shawn’s suggestion about the base is a good one. Therapedic and Comfort solutions both make a very durable and strong foundation with two center supports instead of one (there are links to pictures of them in post #4 here) that may be available from local outlets and there are other good options as well in the foundation thread.
Thanks for all your questions and comments along the way and I’m looking forward to your feedback when you receive your mattress.
Phoenix