if you are worried about the batting shrinking (which really depends on the quilting done on the quilt) why not buy one that doesn't shrink? there are so many to choose from now- you can get ones that don't shrink at all- ones that shrink a little- ones that shrink alot-
out of the 150+ quilts i've made- i've NEVER pre-shrunk a batt- and i've never had a quilt not turn out because of batting shrinkage after the quilt was finished and washed-
and i always wash and dry my finished quilts on regular cycles in the machines- going to a laundry mat if the quilt is too large for my machines.