Snuggle Fabric
JoAnn's carries snuggle Fabric. I don't know if it's exclusive to them but I use it a lot when making pj and lounge pants for my granddaughters. I've used the scraps from the pants in quilts and never had a problem with it. As with any flannel, I wash it first.
They usually have a really good sale in the fall towards Christmas. It's been $2.95 on sale in the past; don't know what it will be this year with prices going up everywhere.