Get this best-selling Slumber 8" Mattress In A Box from $129 with free shipping right now at Walmart.com. This is the lowest price we've seen for this mattress by $10, which we saw back in July! The Twin size drops from $169 to $129, Full drops from $189 to $169, Queen drops from $229 to $189, and King drops from $259 to $229. Better yet, this mattress has a rating of 4.5 out of 5 stars by over 2500 reviewers. Sales tax is charged in most states.