I most often use a sheet for quilt backings as I always machine quilt and sheets really keep the cost down as most quilting fabric in Canada retails between $12-$18 a metre. I always buy King sized sheets when they are on sale and can often get cotton ones for $10. In my sheet bin I know I have a couple of beige/tan mottly sheets which would complement your quilt nicely. It would have to be a very special quilt (daughter's wedding) for me to even think of buying yardage for a quilt backing.