I love the casual style and comfort of a simple pair of flannel pajamas pants. I like to call them house pants. My teen aged son is the one who uses them most at our house. I'm sure you've seen them in the stores and other places. I work in a grocery store, and I even see people wearing them to do their grocery shopping in these days. Some wear their slippers too.
While I'm pretty old school when it comes to wearing pajamas outside of the home, for inside and staying at home, I think they are pretty close to ideal. There sure is no reason to not be as comfortable as you can be when you are at home.
I bought my son a new pair of nice 100% cotton flannel, black and white plaid house pants today and he really likes them. They have an elastic waistband and also a draw string for a perfect fit.
These would make real nice Christmas gifts too, I think. I plan to visit my local fabric store soon to check out their patterns and fabric to see if I could make a few pair for the guys on my shopping list. If I can make them for under $8 - $10 a pair, or maybe even less, I might even make them for some of the girls too.