A king size quilt is at least 95" square (that's with just an 8" drop all around).
Borders around the YBR center would look just fine. You might have a bit of search trying to find coordinating fabrics.
Maybe you can do some sort of pattern in the border as well, as that's a lot of space with just.......fabric.
But it's so nice to know the quilt is really wanted.
Be grateful it's not a California king. :mrgreen: