I make my own layer cake sized pieces quite often. You may have to experiment to see what you like, but, for example, when I do the Double Slice Layer Cake, my favorite way is to use ten fabrics. Let me show you one, and you can see if that might give you enough variety. I tend to go for 3 lights, 3 darks, and three mediums....that equals 9 fabrics. then I just make one more of whichever of the fabrics is my favorite.
This one used 20 10" x 10" pieces. It makes a lap-sized quilt. Doubling that would be easy, since you can get four 10" x 10" from one ten inch width of fabric. You could easily buy 1/3 yard of each fabric you wanted. I lean towards purple and blue, so I tend to do several shades of each. But the possibilities are endless.
Hope this might be helpful...
Dina