Hi kainen1,
If you mean a base (foundation or boxspring depending on the type of mattress) for the mattress then I would put the majority of this extra K into the mattress and less of it into the base. Of course if you mean a bedframe that would hold the mattress and the boxspring or foundation, then the extra k would be justified depending on the materials and design you wanted.
Post #2 here includes the factory direct manufacturers and better outlets that I know of in and around the Bay Area. Some may be a little further away than your guidelines but most are “within range”.
Phoenix