This old thread came up in my search for "bed in mazda 5," looking for pics of a built-in platform to sleep 1 person, about 8" below the rear passenger window sill height.
I've built a flat cargo floor that installs w 2d & 3rd row seats out. With a 3" memory foam on the cargo floor, it's perfect for one 6-footer (I assume the 6'2" clear length at hatch height has been settled. Also, realize we don't sleep at our full height.)
The problem for two sleeping is the 41"width between the wheel wells -- pretty tight for two if you're used to a king, unless you're also used to both turning over at the same time.
I've seen van conversions online that attach a bed for 1 along the side of a larger van, or even a pair of them over-under. The M5 doesn't have the height for two, but one platform about 28" wide could sleep 1, with another on the cargo floor.
Has anybody seen this or something similar?