I have an older set of flannel sheets and absolutely love them.  Not only are they warm and comfy but they easily fit my king mattress that is very deep (18 inches)...with plenty of extra material to tuck underneath the mattress.  I was pleased with the price (reasonable) and the prompt delivery service via Wayfair.  Warning: the first few washings will cause quite a bit of dryer fuzz but never worry, the sheets are still nicely plump!