So I took some tiny scraps and sewed them right on the shirt - no interfacing, no finished edges. I also covered up the Hanes logo because it didn't look dreamy enough. I used 2 blue and white flannel clouds, one on the inside, one on the outside.
Related, the elastic was shot on a pair of my pajama pants. Sometimes I just sew new elastic on top (like this mend), but this time, I had a better idea: I cut off the elastic and attached a new waistband entirely, using fabric from a yellowed, vintage pillowcase. The drawstring has a section of elastic in the back - so much more comfortable than a total drawstring and so much better looking than a total elastic waistband.
To play with fabric like this was so fun and easy - I encourage you to go patch up your pajamas! Apparently, my sleepy look is shabby chic. Who knew?