Since you seem decided on weaning now, then that's the good first thing to start with.
Me, I co-slept and nursed both my kids and let them self-wean. My oldest self-weaned at about 2.5 years, and my youngest at about 1 year old. Each Mom is different and that is fine.
First, since he is 18 months old, how many times a day does he nurse? For how long are the sessions? I imagine, at this time, he probably is not nursing ALL the time, nor "on demand" now?
Is it mainly just before bed time and before naps etc.?
If so, and he not nursing much at this point... what you can do is just nurse ONLY if he asks.... or if he asks, then distract him... ie: stand up, make like you are busy, and don't sit down. Let him know that "in a bit..." will be nursing time etc. That is what some Moms do, and then the child will get distracted and then "forget" the immediacy of it and thus the "habit."
Or, you just go cold turkey, and bear in mind that it won't be easy. It's a transition like anything else. And your boobs may get engorged, depending.
Or, some friends I know, actually put Band-aids on their nipples and would say something like "Mommy has an owee...." or "Milk doesn't work now..." etc. For my friends they said this worked. Their kids were about 2 years old at the time. So it may be age-related.
Or, you just explain that only at certain times, is nursing time.
Or, even while nursing... you lessen the frequency... AND the duration of the nursing. Don't just let him hang-out there endlessly at your boobs. Some Moms count out-loud, slowly, from 1 to 10, and then when they get to the number "10", nursing is over.
As for going from co-sleeping to his own bed in your room... well, that is what we did. And it went fine. We have a futon mattress on the floor of our room, and then I would lay next to my kids on it, until they fell asleep, then went back to my bed. My son is still in his crib in our room...but IF he wakes, I put him on the floor futon, and then he goes back to sleep. For my Daughter... she has her own room and her own bed... and she sleeps there or on the futon in our room. It's fine with us. We are not hardliners about them HAVING to be in their own bed, ALL the time. So sometimes we are still all in the same room, together. My girl says it is like camping. It's no big deal to us.
At his age, probably a crib is better... or he may climb out of a toddler bed and then end up in your room anyway...unless you put a gate in the entry of his room. It will be a transition like anything else, and ESPECIALLY since he has been co-sleeping with you all this time. For my daughter... she was tougher to transition... we made her own room and got her her own bed at about 2-2.5 years old....and it took a LONG time (I'm talking MONTHS) for her to finally be able to sleep without me... but so it was, and we did whatever it was that would ensure her the best sleep. By the time she was about 3 years old... then she was finally in a groove about going to bed by herself. But it was gradual. We did not punish or MAKE her stay there... First I would lay with her in her room, then I'd often just sit in a chair in her bedroom and read or something, sing a song.. .and then it got less and less to where she'd just go in her room herself and then sleep on her own. Gradual is the word, with how we did it, and according to the nature of our daughter. For my son, no problem. He is less clingy.
Since your son wakes up a lot all night to nurse as you say.... is it really to nurse or just to pacify? Is he REALLY "hungry"? Maybe he needs a lovey to sleep with? My son has one and it really makes a difference...then they can self-soothe themselves.
Transitioning from co-sleeping and then weaning from nursing... is also about them self-soothing and comforting and "learning" how to go back to sleep themselves. Each child is different. So just be prepared for this...
Or, speaking about my son, he likes to have a bottle with him in bed... I put water in it and its fine... and it can even be an empty bottle...but the thing for my son is that he likes to just HOLD the bottle and then "twiddle" the nipple on the bottle... this is his way to self-soothe. So along with his stuffed cow... this is also something that helps him to sleep on his own. The thing is... a bottle is like a "boob"...ie: it is where milk comes from... for my son, this was a good happy medium for him. My son weaned from breast on his own at about 1 year old...but he still likes to hold the bottle for sleep time. My daughter on the other hand, self-weaned at about 2.5 years old... and she took a LONG time to go from co-sleeping to on her own.
Well sorry for rambling...the main thing is to allow for transgressions and the transitioning. It is not a "slam-dunk" overnight adjustment. It takes time. Each child is different, so allow for that. Do what is best in your heart and for your son.
Good luck,
Susan