The natural, instinctive state for a human child is next to their parents. In fact, most of the world co-sleeps with their children (often due to financial necessity). In the USA, our wealth allows us to have separate sleeping spaces for our children, however this goes against nature's design.
This is how I have always transitioned my children without CIO:
I co-sleep in my bed with my child and hubby until nursing starts to span out to about 3 hrs at night(about 12 months of age for my kids). Then, I bring the crib into our bedroom and set it up next to our bed, take the side off and lash it to our bed. Then I start nursing my son in our bed until he is asleep, then moving him into the crib. Initially he may only sleep there an hour or so, and then he will come back into our bed. But slowly, he will start to sleep longer stretched in his crib. He is now 18 months and I can nurse him in bed till he is sleepy, but not fully asleep. I can put him in his crib and he snuggles down and is dead to the world, no cries at all. He sleeps about 3 hrs at a time now and I can put him back after nursing, but can reach out and rub his back if needed.
If he follows his sister in stages (and so far, he is), he will be in his own room by the time he is 3. It is a gradual, and yes, slow, way to make your child a secure and comfortable sleeper. They know mom and dad are there and they do not have bad associations with sleeping.
This is from Dr. Sears, who championed Attachment Parenting and is a huge advocate of long term breastfeeding:
LETTING BABY "CRY-IT-OUT" YES, NO!
If only my baby could talk instead of cry I would know what she wants," said Janet, a new mother of a fussy baby. "Your baby can talk," we advised. "The key is for you to learn how to listen. When you learn the special language of your baby's cry, you will be able to respond sensitively. Here are some listening tips that will help you discover what your baby is trying to say when he cries.
The cry is not just a sound; it's a signal – designed for the survival of the baby and development of the parents. By not responding to the cry, babies and parents lose. Here's why. In the early months of life, babies cannot verbalize their needs. To fill in the gap until the child is able to "speak our language," babies have a unique language called "crying." Baby senses a need, such as hunger for food or the need to be comforted when upset, and this need triggers a sound we call a cry. Baby does not ponder in his little mind, "It's 3:00 a.m. and I think I'll wake up mommy for a little snack." No! That faulty reasoning is placing an adult interpretation on a tiny infant. Also, babies do not have the mental acuity to figure out why a parent would respond to their cries at three in the afternoon, but not at three in the morning. The newborn who cries is saying: "I need something; something is not right here. Please make it right."
At the top of the list of unhelpful advice – one that every new parent is bound to hear – is "Let your baby cry-it-out." To see how unwise and unhelpful is this advice, let's analyze each word in this mother-baby connection- interfering phrase.
"Let your baby." Some third-party advisor who has no biological connection to your baby, no knowledge or investment in your baby, and isn't even there at 3:00 a.m. when your baby cries, has the nerve to pontificate to you how to respond to your baby's cries.
The cry is a marvelous design. Consider what might happen if the infant didn't cry. He's hungry, but doesn't awaken ("He sleeps through the night," brags the parent of a sleep-trained baby). He hurts, but doesn't let anyone know. The result of this lack of communication is known, ultimately, as "failure to thrive." "Thriving" means not only getting bigger, but growing to your full potential emotionally, physically, and intellectually.
"Cry…" Not only is the cry a wonderful design for babies; it is a useful divine design for parents, especially the mother. When a mother hears her baby cry, the blood flow to her breasts increases, accompanied by the biological urge to "pick up and nurse" her baby. ("Nurse" means comforting, not just breastfeeding.) As an added biological perk, the maternal hormones released when baby nurses relax the mother, so she gives a less tense and more nurturing response to her infant's needs. These biological changes – part of the design of the mother-baby communication network – explain why it's easy for someone else to advise you to let your baby cry, but difficult for you to do. That counterproductive advice is not biologically correct.
"It…" Consider what exactly is the "it" in "cry-it-out": an annoying habit? Unlikely, since babies don't enjoy crying. And, contrary to popular thought, crying is not "good for baby's lungs." That belief is not physiologically correct. The "it" is an emotional or physical need. Something is not right and the only way baby has of telling us this is to cry, pleading with us to make it right. Early on, consider baby's cry as signaling a need – communication rather than manipulation. "
K., Cape Cod Breastfeeding Moms, MyMammasMilk.com