Futon unboxed easily and has puffed up nicely. No issues with stitchingstainssmells like some customers. Puffed to 8” over 2 days and is very comfortable. 
We have had many futon mattresses over the years and you can’t measure them like you do conventional as they are soft sided. The strip around the outside of the mattress IS 12” - then subtract 1” for seam allowance, and remember that the sides bulge. So 8” hight is normal and expected.