Okay, so maybe this is me trying to find an excuse to stay in my pajamas because I've managed to successfully stay in bed this entire holiday season -- an achievement you're going to have to pry out of my cold, dead hands, but consider this: covert pajamas.
It's usually pretty easy to figure out when someone's in their nightwear. The only people who wear onesies as normal clothes are babies and geniuses who realize babies know what's up. Women's traditional clothing are plagued with thin straps and a God load of lace. Then there's the comfortable stuff that's been marked by years of takeout food and runs in the laundry. We exchange clothes that can worn outside for clothes that tell anyone and everyone exactly how dirty our beds are.
The trick to combining the comfort of your cheeto dust mattress diving suit and an actual outfit is cotton. Cotton is a pretty strong fabric. It's hard to stretch out unless you're trying to on purpose, which means it keeps it's shape for a long time. Additionally, it's pretty comfortable, so you can find some that feels like pajamas.
The more similar your cotton clothes look, the more they look like they belong together, like you bought them as a set. Instead of just getting a cotton t-shirt, try and find a cotton tank with some drawstring pants. When you buy cotton, try and make sure it matches as much as possible. It looks more like you put thought into an outfit and less like you left the house without changing.