It's a fairly good size already at 71"x81" ...... big enough to make it usable on a bed as a "quilt".
However, we often now think of quilts as being "bedspreads",
and I am guessing that you are maybe wanting this larger, for that purpose?
My suggestion is like the others, to not try to add to it, for fear of detracting because of the differences in added fabrics. Instead, if you are wanting it as a bedspread type of quilt to show it off ..... Put a plain quilt on the bed as your bedspread, per se. I have often used the plain backside of a quilt for this purpose. Then lay your finished quilt over the top to show it off.
The binding could present the same challenge as adding in fabrics for the body of the quilt. Audition some possibilities. I agree, with others that a solid black may be too harsh. Perhaps a tonal would work, and not necessarily black or dark. Try some other colours and see what looks best. My first instincts are green, blue or a charcoal. Maybe even a darker rose. You might even find a print that would give a variation in colours, and as narrow as binding is, it would not show the print, and just give a nice blendable binding of assorted colours.
Lots of possibilities ... take your time and do what is right for you!
Maybe you already have something in your stash that would