allswell california king mattress. This Allswell California king mattress is 3 months old. It’s in perfect condition because since the professional unboxing it was encased in a waterproof 360° mattress cover. It’s a medium firm but just did not work for us. Instead of paying $593 for the Cal King mattress and tax, we’re willing to let just the mattress go for $399 or the mattress AND the 3 inch Cal King Memory foam topper for $450. The whole package costed us $717.