I just finished backing a couple lap quilts with flannel. I used Mountain Mist (I think that is the correct name) batting instead of my usual White and Natural. The quilt is not heavy at all, just right for lap use. I did wash my flannel in hot water and dried it on high heat in the dryer.
I would recommend using a good quality flannel if you can. I used flannel I got from Walmart and it fuzzed quite a bit. I don't mind since it is for us to use but I would have been disappointed if I were giving the quilt away.