I've done something similar, when I wanted a warmer lap quilt. I made the top and did a lot of decorative quilting to the batting, then backed it with a fleece fabric, and quilted through all the layers around the blocks, so that the fleece didn't pull away from the top quilted sandwich. It measures 45 in x 65 in, and I managed quite well with it under the machine. The machine had no problem going through all the layers, and its warm and cozy in the winter months.