You wanted to know how you can wean your almost-2-year-old from breastfeeding, and he's only nursing at night. And generally speaking, when a mother weans, she should cut out 1 feeding every 2 to 5 days, slowly decrease the amount of time that she lets her baby nurse, and slowly increase the amount of time in between feedings. And so basically, weaning is a process that usually takes 1 to 2 weeks, but the way you implement these principles is going to depend on how often your baby is nursing at this point and the time of day.
You mentioned that he's only nursing during the night. And so let's say that he's nursing twice during the night. To start, try cutting out one of those feedings, and then slowly decrease the amount of time that you let him nurse during that one feeding each night. And after several days to a week or so, try cutting out all feedings during the night. And this will slowly send your body the message that it needs to turn the milk-making factory off. You may find that you wake up really full in the morning after not nursing your baby during the night. And if that's the case, then just manually express a little bit of milk or pump off enough to the point of feeling comfortable. But don't empty the breast, because that will stimulate your body to make even more, and that's what you're trying to avoid.
Now, when weaning a baby or a toddler from nursing, you need to replace those nursing sessions with nourishment if it's during the day. For example, if a baby is weaning during their first year of life (like before the first birthday), nursing sessions need to be replaced with formula to make sure that the baby is getting what they need. Between the first and second birthday, a baby needs to drink whole milk, and so nursing sessions would be replaced with whole milk. But because your son is only nursing during the night, you don't need to replace those nursing sessions with anything unless his pediatrician has said that he needs night time feedings. And at 23 months of age, most toddlers don't. They should be getting the nutrition and hydration they need during the day. And night time nursing sessions are probably just a source of comfort for him.
So in order to teach him how to self-soothe and to go to sleep without the help of a nursing session or from you, you can sleep-train him. And this is going to involve "crying it out". And this is basically where you put him to bed fed, and changed, and loved, and if he wakes up and wants to nurse, then you teach him how to self-soothe by "crying it out". And you can do this for as long as you're comfortable with it. Of course, you should check on him if you feel like he's crying because he has an immediate need, or because he's in pain or something, but if it's just because he wants you, then let him cry for a little while before you respond to him. And after doing this and being persistent and consistent for 4 to 7 nights, then he'll get the message that crying doesn't get him what he wants most, which is you, and he'll learn how to self-soothe.
If this sounds a little bit harsh, then you can try a more graduated approach where you go in his room and reassure him that you're there, but resist any and all urges to turn on the lights, talk to him, pick him up, and just turn around and walk back out of the room. Some parents find that this works well, but others find that it just makes it harder, because the baby screams even louder because the parent came in the room. So if you do want to try this method, first, give your child about 5 to 10 minutes before going in his room, and then reassure him that you're there, walk right out of the room. And he'll probably continue to cry, and if this is the case, wait 15 to 20 minutes the next time, and then go in and do the same thing. And then if he's still crying, wait about 30 to 40 minutes before going in, and incrementally increase the amount of time you wait before you go in and check on him. And again, be persistent and consistent about it for 4 to 7 nights and he'll eventually get the message that he's not going to get what he wants most, which is you, when he cries.
Good luck with it, and if you have more questions for me in the future, feel free to ask them on our Facebook page at http://www.facebook.com/IntermountainMoms, and recommend us to your friends and family too.