For many years, I've been the go-to gal in my family for all the pyjama pants at Christmas. I have a big family, so every year, it's dozens of pairs of pj pants, all in different sizes. When you do that many, you start to hone your technique. A few years back, I finally committed my preferred method to paper, complete with wonky sketches (and some drawings borrowed from pattern directions).
It looks sort of like this:
and you can download the pdf
ETA: No, I don't really have a favorite pyjama pattern. It all depends on how you like your pants - wide leg, tapered, cropped - you have to find your own favorite. However, you can take a pair of comfy pyjamas from home and trace around them to make your own pattern. Just be sure you flatten each section completely as you trace, and then check to be sure your parts match up on paper before cutting them out of fabric. And don't forget to add a seam allowance!