Pstein,
I have a pretty high opinion of OMF. I think they have excellent value, and the shopping experience there is pretty good with no high pressure sales people. I knew they had discontinued their pure latex bed, and their Serenity Latex offering didn't have quite the setup I was looking for.
You're spot on about latex mattresses being heavy. I would go further and say they're insanely heavy. The guys that delivered my mattress worked for a local company who moves mostly latex mattresses, but they were still struggling to manhandle the thing to my house and bedroom. The combined weight, flexibility, and relatively compliant edges make latex hard to move around.