Babies that sttn

For those with babies that sleep through the night (STTN), do you swaddle your baby? How old are they and where do they sleep? My baby is 7 weeks old and sleeps swaddled in Rock n play and will do one 4-5 hour stretch at night.  I'm wondering if she's sleeping a good stretch because she's swaddled or just because she's big enough now that she is fuller longer.  I would love to hear from other moms (ESP those that breastfeed since I know formula can keep them fuller longer)