Does Costco sell mattresses and box springs in the store itself?

Yes. You can take it with you or pay an additional delivery fee.

We bought our mattress from there but had it delivered. It was super heavy so we payed for the delivery and haul away

8-9-22. Per the NW San Antonio's Costco website today they do have varying lengths, widths/sizes, hybrid ones and more. Definitely - call before heading over as stock always varies.

It is hit and miss. They do periodically but I haven't figured out when to know when they do except to call your local store and ask before you go