Here are some I would consider:
http://www.swatchandstitch.com/thequ...-diamond-quilt
https://www.craftsy.com/quilting/pat...-stones/101806
https://www.anniescatalog.com/detail...prod_id=134319
I would probably consider the first two for flannel. The last one is beautiful, but may be too intricate for flannel.
Working with flannel is a little different; simpler patterns work best with it. I like to wash and dry flannel in the dryer twice to make sure it has finished shrinking. After that, I recommend using a heavy starch on it before cutting. I like a 1:1 mix of Sta-Flo liquid laundry starch and water. I paint this on the yardage with a large wall painting brush, wait a few minutes to make sure it penetrates the fibers, then dry in the dryer and iron with steam. Makes the flannel very stable. Flannel creates a lot of lint, so I would recommend thoroughly cleaning your machine (bobbin area and under the throat plate) after every couple of bobbins. Half-inch seams are better for flannel than 1/4" seams, to prevent fraying. Keep that in mind when selecting a pattern.
I often refer to this website for deciding on a quilt size:
https://www.quiltingcompany.com/sugg...hm-welcome-new
Just don't do as I did the first time and calculate the size based solely on mattress size; scroll down to get their recommendations for quilt sizes for different beds. I would think you would want something suitable for a twin or twin xl bed size.
https://www.quiltingcompany.com/sugg...hm-welcome-new
Edit: For the "Simply Cool" quilt, I see that it is actually simple enough to make up in flannel. If you wash and dry the flannel twice and starch it heavily before cutting, as I described, you could get away with 1/4" seams. Just be sure to quilt moderately well (quilt lines 4" apart or less) to reduce stress on the seams. The more quilting on it, the less stress on any given seam. For quilting thread, I would strongly recommend polyester (Glide or Bottom Line) because it will not stiffen the quilt even with close quilting. My experience with cotton thread is that close quilting can make a quilt stiffer and less cuddly.