i make 10-20 flannel quilts a year- and back even more- i love working with flannel!
the only things i would suggest is lengthen your stitch length a little- baste well- use a good quality batting- i use hobbs heirloom 80/20
put in a new sharp needle.
i tend to not understand people's problems with flannels- i've never had one that was (stretchy) or became wonky-
i've added a couple pics of flannel quilts- that i hope shows the quilting