K.,
The most difficult thing in the world, to me, is listening to my little one cry. We too co-sleep and are on the 17th month and going strong. My husband and I decided to co-sleep since our little guy is a nursing baby. We are going to the two year mark and will begin the transition process of converting him from our bed to the crib. At the 1 year mark, I moved his crib from our room into his nursery. He naps during the day and from 7pm until we go to bed at night. Then, I transition him into the bed with us. He is still in the night nursing mode, so it will be a while before I try leaving him in the crib when we go to bed at night.
Right now, he has a little dog we named from his favorite book "Skippy". Every time he goes to the crib, skippy comes with him, along with the same blankets. One blanket is rolled up to rest next to him and the other is a small blanket to place over the bottom half of his body for comfort.
I do not believe in 'let them cry it out'. Everytime someone tells me that, it brings one question to mind. "How would you feel if you were a little child in a dark room with shadows and unfamiliar noises and someone told you to cry it out?" If you ask any psychiatrist, they will tell you that comfort from a mother builds their trust and empathy towards others later on in life. Promise you, children who were left to cry it out are more apathetic than empathetic as adults.
Every habit that we try to build or break takes 14 days. You are telling your little one that he/she must change this habit of sleeping cozily with mommy and now, move into another room and sleep in a bed on his own. This will take the act of a strong willed mother sticking to her guns and at the same time be very empathetic in the process.
Children are comforted by their mothers nonverbal and verbal communication. You simply walking in the room starts to comfort the little one and then making comments in a comforting voice...I would recommend starting a process in the evenings..for example, bath time 1 hour prior to sleep, read the same book 10 minutes before going to bed, grab a stuffed animal (small), tell Daddy night night, and begin the bed time at the same time every night.
When he/she wakes up in the middle of the night, try comforting as much as possible (your own style). Lay down with the little one for a few minutes, if he/she gets back up, place back in the crib and say let's go night night...after a few minutes if this does not work, leave the room for a couple minutes, crying makes them sleepy within 2 minutes,then, go back in, place back in the crib and say again, let's go night night...if this does not work, make a place on the floor in the nursery and rest with your little one. Then, when they go back to sleep, place back in the crib. Make certain you have a night light in the room too. This will help the little one not be so scared when waking up in the new environment. It is going to disrupt your sleep for the first two weeks, but he/she will eventually know that this is my new 'habit' sleeping environment and I must get used to being here by myself at night.
Good luck!