1. Using a cotton batting such as Hobbs 80/20 or Quilters Dream cotton will help when you are ready to machine quilt the top, because cotton on cotton doesn't shift as much as cotton on polyester does. You'll still want to baste; check out "basting" using the search feature on the board for discussions about different ways to do this.
2. "Washed" batting has much fewer wrinkles out of the package and tends to shrink less. "Wash" batting by soaking it in your washer on lukewarm, drain, gentle spin, 'air' or 'lightly warm" damp dry in dryer about 10 minutes, fluff out over the sofa before you head to bed for the night. It'll be dry in the morning, ready to layer.
I offer you a tip I've frequently shared here for maintaining an accurate, consistent seam allowance, my little gift to welcome you to the board: