kona cotton solids are nice fabrics- and you can get them in different weights- from (calico's) on up to broadcloth & canvas.
check out on line shops that have swatch offerings---fabric.com will send you swatches of fabrics before you commit to yardage- they have a good selection of solids.
why do you not want to use a muslin? there are some very good quality-beautiful muslins that many fabulous- award winning quilts have been made from.
a white on white- cream on white fabric may be a good choice with batik's- they would add some movement-texture without distracting from the appliques.
there are so many choices-
it never hurts to ask (even on line shops) about swatches- some shops will happily send you a swatch- but they may not advertise that---never hurts to ask....but i know fabric.com does---
i hope you find just the perfect background...and show us what you are doing soon
