These are called The Sound of Music Pants because they are made out of a pair of curtains. I made them from a pattern I drafted years ago from an old pair of pants that were a gift from a friend who had made them herself and was bored with them. The cut was so comfortable and flattering that when they eventually died I took a pattern from them before retiring them to the rag bag.
I have used this pattern for pajama pants, track pants, anything over the years. It’s my default basic pant pattern. With the elastic waist and wide legs they are about as comfy as pants can be. Pretty much a way to legitimately wear pajamas in public!
The original pants were made from stretch fabric. These aren’t so I added a cm to the pattern up the outside leg and narrowed the seam allowance to make sure they could fit over my bum easily. Next time I think I will also do my standard addition of a few extra cms at the top of the back to accommodate my rump.