I just purchased a 176S and am converting the bed area to a full sized bed instead of queen.
So I've got a brand new, never used queen size mattress made by Mastercraft Inc in Lagrange Indiana.
It's 5-1/2 inches thick x 60" x 80". Sort of a pale yellow, champagne color. According to the label it's made of Urethane foam.
When I tested it, it seemed comfortable. Soft but with the hard OSB underneath, it had support.
I am asking $50 for it but you will have to pick up. I'm in Seattle. Please email if interested. email@example.com