Hi jambro,
The Reverie, Ergomotion, Leggett & Platt and others all have solid surfaces. I don’t know what the surface is made of (probably MDF or Plywood)
There are a few other adjustable beds that have a ventilated surface such as http://www.axelbloom.com/los-angeles-beds/
As you can see in post #10 here though … I think that a slatted foundation is the best choice unless there is a compelling reason to choose something else. In my own case … wanting an adjustable bed was a compelling reason and make any additional risk of a less breathable surface worth it to me.
Phoenix