I may be over thinking this... but would there be any issue with a three month old using a Sposie overnight? DS sleeps through the night but by 3am has soaked all the way through his sleepsack. I hate to wake him up just for a diaper change (he won't sleep through it, then will need rocked back to sleep).
DS has a paralyzed vocal cord, a g-tube and had aortic augmentation at five days so I am very sensitive to waking him up unnecessarily. I deeply believe healing is linked to rest.