Used the Purple matress for 8 years. Really liked it. Switched and got an Earthfoam after we lost the purple one in a house fire. Earthfoam firm with medium topper was good for us. Interesting to hear about this arm channel thing... no idea if that would work or not.
It's definitely got my attention!
I read into it more. It has some pretty terrible reviews on reddit. Take that for what it's worse and it was from a few years ago. But most people saying it ended up causing a lot mote strain and pressure on their neck..
They kind of address that on their website that you must have proper pillows and the thing that drops into the slot for good head and neck support. I also really like that 100 night risk free trial. If you haven't gotten problems by then I would think you would be good.