What kind of pj's should I get?

I am buying on down long sleeve shirt PJ's with long pants and I am wondering wether or not I should get them in flannel or cotton. Flannel is more expensive and cotton is cheaper. The problem with flannel is they are great to wear around the house but I might get sweaty with them under the blanket. Cotton is ok because they will feel good under the blanket but I might get chilly around the house. P.S. I have to sleep with a blanket on