OK, I will add a note here that although I had thought I had weaned my 23 month old daughter, she actually still does sometimes 'feed' if she comes into out bed. Not sure she's drinking much but it beats getting up at 5.30 am and I'm happy that if she wants the comfort and familiarity, I'll give it. What I needed to change was the co-sleeping all night and feeding to sleep.
Our breastfeeding relationship up until 21 or so months was frequent, through-the-night, always feeding to sleep. I was getting increasingly ragged and yes, it was affecting my relationship (although my husband is, was and as a part-time SAHD incredibly supportive of co-sleeping/AP style. I also didn't have a period until a month or so ago and I want to TTC.
Between months 19-20 I'd cut down the day feeds (I work three days and DH used to bring her to where I worked and I'd feed her at lunchtimes) and that actually went well. A bit upset here and there but distracted and cuddled and we still slung her (still do) so she felt close.
Basically the serious weaning was tied up with the sleep. My daughter's talking and understanding are good so I basically took her to Ikea, got her to choose a bed and we did up her room properly. Really made a fuss about it. Also talked to her about feeding to sleep and how that was ending but that I would still feed her before a story.
She was excited and seemed happy so I pressed ahead. Bath, bed, feed then a story then popped into bed. I stayed at the end of the bed and made generic soothing noises and stroked her while she cried (angry rather than desolate) for an hour. She slept through that night. I fed her in the morning.
I continued this for about a month and after a holiday where we'd regressed back to feeding to sleep (I kind of had to, share villa with friends and she woke because she was in our room) when we came back I just decided that I would stop. In fact she made it easy by not asking. But she asked the next night and I demurred.
She's had cows milk, water from doidy's and isn't a huge drinker, but a good eater and eater of fruit so this whole weaning process wasn't about meal replacement, or getting a certain amount of ounces.
On an emotional level, now the dust has settled, I can see that although I gave her a nudge we picked a good time. But it was hard letting go - some days I'd fed 18 hours out of 24 (she was a bit prem and dinky so I would feed very often) and although the 1-2 hour wakings were completely doing my head/sanity in, the whole thing shaped my early relationship with her and there were some really truly lovely times (oddly at 3am)
But I'm happy that we did it (I would have probably left her to self wean completely but for the fact it was suppressing my fertility). And she seems happy. And if she wants it in the early hours (not on nights where I have to get up at 5,30 am though) she can have it.
Good luck. The anticipation of it for me was worse than doing it.
What I wanted to add was that at 18 months if you're feeding to sleep or feeding for naps (the times I was pinned to the sofa unable to get drinks/pee...) and haven't had a night off from bedtime duties it can seem bleak and never ending. And yes, you can feel bitter that all your non breastfeeding mother friends are out having fun, leaving their babies with grandparents, husbands can get them to bed.
I honestly thought I'd be doing this until she was three.
But their understanding and ability to accept that the frequency has to change is greater than you think from 18 months on. Their needs drift to becoming wants. And sure, if you still want to feed 4 times a night then that's fine and I did this while working part time with very early starts. But if you want this to end, then don't feel too bad that you need to give them a nudge. I'm pretty AP but something had to give for me too and actually I could handle a bit of upset obviously it's nothing like CC but soothing them another way on the few days it would take as they get used to it isn't going to harm them. And if it really doesn't go well, put it off for a month or so.