home improvements - maid's room

Any idea where I can get mattress for sale? I need to buy one soon, not for our use but for our helpers room. You see, the current mattress they're using kinda small. single size. And I feel bad everytimne I see them trying to squeeze in one bed. Though it was ok few years ago, when we just had one helper. However, with our increasing family size ...we decided to get additional helpers. From one helper six years ago, we now have three house helps. Thus, the husband and I thinking of upgrading their present bed, from single to double size bed.