That's a good plan. I don't usually do borders except on panel quilts, or when I need the top to be bigger, like you are thinking.
I just got done sandwiching some quilts. I have 4 Boom quilts up there to quilt, plus another set of Boom blocks. I had a lot of big batting scraps, so I cut 13" squares of batting to do that last set of blocks QAYG. Plenty to do!