I just changed out the mattress in our Greyhawk 27u. I'm so sad that I waited 2 years to get this dome.
We ordered from Tochta. It was easy and fast (14 days from internet order placement), and you can order the thickness you want up to 10". They also sell custom fit protectors and sheets. Price was high but reasonable and we love the mattress. We have only slept on it 7 nights, but it has been a great upgrade.