I adore these PJ's so much. This one is my second pair and they are still delightfully cozy! I ordered a large since I typically wear that in JessaKae, I feel like I could comfortably wear a medium though.
For reference I'm a 36D. 5'4". Size 6/8.
It has an oversized fit, which means the pants are way too long for me so I'm having to alter the pants- otherwise they get dragged and get so dirty!
ALSO, make sure to wash it before you wear it officially- both of mine had a really funky scent to them, but washed out easily.