Love this mattress. I am a Senior and managed to unpack and put on a kingsize bed by myself. At first I thought that the cover was too big for the mattress but learned that you should leave it to regain the shape before using.  Once ready to use the cover is fitted properly.  A good way to judge if ready to use.  I left it for 2 days and when I measured it was 8".  Maybe others weren't leaving long enough before using.It is firm bot really helps for back issues.