This double mattress is 2.5 years old, it's a spring mattress with memory foam top layer, super comfortable, and fits on any Stanford issue double bed. (I was able to fold my Stanford blue rubbery mattress and fit it under my bed) I bought it from Ikea for $400, and am looking to sell it now.

Here is the description from Ikea:

SULTAN HANSBO spring
mattress, white.
Pocket
springs
25-year
limited
warranty
Memory
foam
• A 1⅝" thick memory foam cushion responds to
your touch and temperature, molding to your
body shape for precision support.
• Active pocket springs respond independently
to cradle your body and help relieve pressure
points, while keeping your spine properly aligned.
• The pocket springs are individually wrapped to
insulate movements so you don’t disturb your
bed partner.
• Thickness: 11"