Co-sleeping refers to any sleeping arrangement in which the primary caregiver, usually the mother, sleeps within close enough proximity to her infant so that she and baby can respond to each other’s sensory signals and cues. Research by Dr. James McKenna, Director of the Mother-Baby Sleep Laboratory of the University of Notre Dame, showed that mothers who sleep close to their babies enjoy a heightened awareness of their baby’s presence that protects him. The mother is more aware if her baby’s well-being is in danger. The baby also experiences a less deep state of sleep, which enables him to awaken more easily if breathing difficulties arise.
There are a number of options for parents who would like to co-sleep. First, your baby could sleep in the bed with you. It's recommended that the baby sleep between mom and a wall, and not beside dad because dads may not have the same instinct to not roll over onto the baby. The baby should be beside a wall so that he cannot roll off of the bed. Or, you could use an infant in-the-bed co-sleeper like the one below.
You could also consider side-carring a crib, which is where you take off one side of the crib and put the crib against your bed, To learn how to sidecar a crib check out this site:
If you're worried about baby falling in the crack between the crib and your bed you could use Magic Bumpers, which have many uses. We still use them when we're traveling and the kids have to sleep on the floor. The bumpers create a nice bed area.
If you'd rather not deal with the hassle of side-carring a crib, you could buy an Arm's Reach Co-sleeper like this one:
I always wanted an Arm's Reach Co-sleeper. We ended up using something similar for our daughter, but much less expensive. It was the Fisher Price Rock and Play Sleeper. My daughter slept completely through the night in this thing. Every night. But boy did she nurse like crazy during the day! She stayed in it for 5 months and then graduated to a crib in our room. Here is the Rock and Play Sleeper:
This is the Amby Baby Hammock and it has great reviews. It's cozy and it swings vertically, to simulate the movement of mother's womb as she walks. Great quality but quite a price tag.
So, how long should you co-sleep? That's different for everybody. I don't think a child should have to sleep alone if he/she doesn't want to. Maybe six months, maybe six years. Every child and family is different. And co-sleeping doesn't have to mean the child sleeps with you in your bed or right beside you. For some people co-sleeping simply means having an extra bed for your child in your room in case he/she wakes up at night and wants to be near Mom and Dad. If you think that six years is too old just remember that many people in the world live in one-room homes their whole lives and in essence co-sleep their whole lives!