Hi Pam,
What a nice quilt. I like the polka dot border.
You could have the polkda dot border in say a 2" border first.
Then put a thin 1/2 inch folded fabric border in the
Breast Cancer polka dots fabric.
Then follow with a 3-4" outside border.
I would have the binding match the outside border.
If fabric is in short supply, I would then think about making the binding a scrappy binding using all of the fabrics used in the quilt.
I would have each scrap be in varied short lengths with the fabrics repeating so they continue around the quilt.
Please keep us updated as you progress through your project.
Pam M