Hi welshie55,
Congratulations on your new mattress 
I think you did some good research and ended up making a great choice. Best of all of course you still have options to customize the mattress after the purchase if that becomes necessary.
I would personally “vote” for slats (see post #10 here).
I’m looking forward to your feedback once you’ve received your mattress and have had the chance to sleep on it.
Phoenix