The building is metal with a straw roof and supports made of bamboo. It has a sign on the front that says Mattresses & Then Some. They went here to get a matress for Mr. Krabs.
The inside of Mattresses & Then Some has many different mattresses inside. They include:
Race Car Mattress (also a driveable car)
This is one of two mattress stores in Bikini Bottom. The other is Mattress Discount. Surprisingly, both stores only appear in Season 4. However, this mattress store appears to be a lot larger than Mattress Discount.