I would do flannel with cotton batting. It will wash well & not be too hot for the little one. Babies aren't supposed to sleep with covers anymore, so I find unless I add a sleeve, the first use other than for pics is at 4-6 weeks when they do tummy time. The flatter material, in my opinion, is easier for the babies to tolerate and push up from than a fleece. That said, of course they will love touching the fleece, so it all depends on how it will be used. But flannel is plenty cuddly enough and cotton quilts get softer and softer with each wash, even if it's quilted at 1" apart which is what I do (usually with all quilter's cotton, but I make changing pads with flannel and have done client quilts with a flannel back and 2" lines and those were also very soft after a couple washes).