I think it depends on how heavy and warm you want the quilt to be. Personally have never made one without using something in between. Flannel works really well, if you don't want it to be overly heavy. If I am reading this right you are putting denim (jeans) on one side and minky on the other. I would also go around each of these squares twice, for reinforcement, at your half inch seam. Just saying what I would do, but the final decision is yours to make.