most batting will (fluff) a bit when washed after you finish your quilt. cottons and wool batts fluff the best.
the heavier the quilting (density) the stiffer the quilt will be. some people quilt very heavily and use the thinnest batting they can find because they want their quilt to be flat...stiff....
others (like me...and you) want the quilts to be fluffy and warm...warm & natural fluffs up nicely and can be quilted up to 10" apart...the less quilting the more area there is to fluff.
flannel fabrics also wash up soft and fluffy