in the past I have purchased the flannel sheets from Costco but they didn't seem to have the same ones this year so I bought these. These fit my thick mattress better with its deep pockets, and the material itself seems to be thicker than the ones I got from Costco. my only complaint is that the flat sheet is not exactly square and one of the pillowcases also isn't square. 
the Costco sheets would only last me one winter season before they stretched out and just didn't have the same feel. Mabe these will last longer.