We ordered a Tuft and Needle king-size mattress (https://www.tuftandneedle.com/mattress/shop) for $750, and the mattress that arrived is ~4-inches less wide than it should be (~72 inches rather than 76 inches). The mattress doesn't fit the standard king-size bed frame we have, but it would be perfect for putting on the floor or for use with an adjustable bed frame. The mattress is unused (we just unwrapped it a few days ago) and available for pickup in Mountain View ($250).