Got mine on Amazon.
I'm back from my 3 day road trip which included 2 nights sleeping in the Model Y with another person on the Exped 10 Duo. I'm 5'11" 180 pounds, pretty average build. The girl I was with is a few inches shorter, and takes up about the same amount of space. We slept great. She was actually excited by how comfortable we were able to get. The mattress is very comfortable and we both had enough space to sleep without touching each other if needed (back to back sleeping on sides). We plugged into 14-50 outlets at RV parks both nights, and cranked the AC down nice and low too keep it cool and comfortable all night in the car. The most cumbersome part of camping inside the Model Y is organizing your stuff before hopping into the back to sleep. Trying to change/get clothes ready for the next day, or getting things out of your bags (ours were on the floor behind the front seats) while the mattress is laid out is a bit of a challenge. But we had no issue making it work.