Remember that co-sleeping and bed sharing are two totally different things. A lot of people confused the two or misuse the term. Co-sleeping is sleeping in the same room, but baby has his OWN BED. Bed sharing is everyone in the same bed together.
The safest way for your baby to sleep is flat on their back with no loose blankets or bumpers etc. The reason flat on the back is safest way for baby to sleep. New research is coming out regarding the development (or lack there of) of babies jaw. Sleeping in carseats, swings, in the crook of mom's arm etc. push the jaw forward and can block breathing airways. This is why the AAP does NOT recommend placing your baby in swings, rock and plays, sleep positioners etc for sleeping.READ: http://www.kidsindanger.org/family-voices/preston
I know that some babies have to sleep this way because of reflux, but if your baby doesn't have any health problems, your baby should sleep flat on the back.
"The increased incidence of oxygen desaturation in premature
infants placed in semi-upright infant car seats compared with lying in
cots15,16 has been shown to be associated, at
least in part, with flexion of the head on the body and marked narrowing of the
upper airway on respiration-timed upper airway
X-rays.16 Although most of these observations
were made in preterm infants, there is evidence that the similar albeit lesser
frequency of oxygen desaturations in term infants restrained in car
seats17–19 may also be related to forward
slumping of the head on to the chest and consequent pressure on the
chin.20 Indeed, even at term, displacement of
the jaw with oxygen desaturation can be obtained by any pressure on the chin,
including forward flexion of the infant’s head onto its own chest in some
Hope this information is helpful!