Another thing you can do is make the same block but vary the size. Make some 3' 6", 9", 12". Lay them out and see what you need to go between them! 9 3" blocks together would make a 9" block. 4 6" blocks together would make 12" 9" + 3" would make a 12" blocks. All kinds of various sizes would keep the blocks fresh! Even just strips of fabric interspersed with the blocks would change the whole look of the quilt.