Hi kbeaub,
Just speculating because I don’t know all the details of how they ship but I think that the bedding package is included with the mattress so these may arrive together.
Also speculating … the adjustable bed has to be shipped with truck freight rather than UPS which can take much longer (especially over holidays) from initial shipment to destination but of course they could probably tell you more about this as well.
I’m not what I would consider to be a bedding expert but if I had my choice in sheets I would choose between bamboo or other viscose fibers (for the soft feel and moisture wicking qualities of viscose) … high quality Supima or Egyptian cotton (in a medium/high thread count not the highest possible thread count for breathability and overall quality and durability) or perhaps best of all Linen (flax fibers) because of their coolness, strength, and how they soften and become more comfortable over time.
There is more information and links to some resources for sheets and bedding in post #26 here along with post #3 here.
I know that Costco also has some good value cotton sheets from time to time.
Hope this helps
Phoenix