Guys, I bought this: https://www.amazon.com/gp/product/B071X7C4TB/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

I'm not a big guy (5'11" 157lbs) and my arms kept falling off the sides, so unless you are a side sleeper or level the area around this particular mattress, your arms will sag off the sides.

So I then went and bought this: https://www.amazon.com/gp/product/B018APB3TI/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

And found it to be so much better in terms of my arms being able to rest at my sides...but even more how much more lower back support I was given vs that of the tri-fold. The tri-fold felt like it was actually straining my back due to lack of support so I had to put my https://www.amazon.com/gp/product/B014AQ90A0/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 under it, and that only marginally helped.

So I'm ditching the tri-fold.