I would prewash all fabric to get maximum shrinkage first.
Also, if you are worried about stretching, do a simple stay stitch around a block or piece of fabric. 1/8" should be good and would be covered by a 1/4" seam.
Anytime we don't use fabric all from the same line, we are in essence mixing fabrics. Most of my quilts use different fabric lines.
And, if you have some one who likes to feel the different textures on a quilt, like a small child, minkee, flannel and corduroy would differently feel good to them.
After I retired, the first two quilts I made were blue jean quilts that I made using my kids old jeans and mixed with flannel and bandana material.