Unless you love making bedskirts I would buy one.
I just made a King Log Cabin for us. The overhang is about 12 inches on each side and we have plenty of room so that we don't pull the covers off each other.
I don't believe you are overthinking though. A King is a really large one and you want it right.
PS. Sorry I didn't realize you have a Cal King. Mine is a regular King. Big enough for Paul, me, and the cats
