Plan how you are going to quilt these, and what type of batting will go with your plan.
You probably don't want to quilt over the tshirt's design... :wink: I could be wrong, but when shopping for batting, the largest quilting requirement I have found is 10". You don't want the batting bunching up on you after use/laundering.
Maybe well washed flannel, a light weight blanket, or a heavier backing without any batting would work if you want to keep the blocks bigger and the quilting further apart :D:D:D