hi Goldenbear ... very long post from me coming your way, I hope it's helpful and apologies for the sloppyness, it's so hard to remember everything and in what order especially when you have a dc who is not the best sleeper in the world.
I could have written your past almost to the letter. I have been doing gradual withdrawal with my dd for some time now and finally (fingers crossed) we are getting somewhere, BUT it has taken a long long time. Here's our backround and the method(s) we've been using. I'm not sure how much if any is relevant to you and your situation but I know from experience that even if one thing helps it is a step closer back to feeling like a normal human being rather than a zombie at the end of a it's tether.
DD (2.11) and I have been (fully) co-sleeping since she was 18mths after I got fed up with constantly getting up in the night. Since dd was about 2 yrs old we've tried to get her back into her own bed 4 or 5 times, each time something happens (usually illness) to bring her back into my bed. We tried all sorts, giving her more milk, reducing her milk, changing from full fat to semi to skim back to semi. We tried earlier bedtimes, later bedtimes, no tv before bed, "gentle" tv programme before bed, big tea, little tea, later tea, earlier tea, bedtime snack, no bedtime snack,sleeping on the floor in her room, not sleeping in her room. We have always sat with her until she falls asleep ... which these days is about 5 mins as she no longer naps. The only thing we have never done is leave her to cry - that's not for us.
For the last few months (yes! months!) I have been sleeping on the floor next to her bed. Same bedtime routine. When she woke in the night a quick pat (usually but not always) and a Ssshh sleepy time got her back to sleep quickly. The first night I did this she woke up every half hour, the second night every couple of hours, the third night only a couple of times and so we continued in this up and down way (but never as bad as the first couple of nights) we had got to an ok place with her waking once or maybe twice a night and me getting a reasonable amount of sleep. I was reluctant to try and move on from this as did not want to go back to sleepless nights. A couple of weeks ago we went on hoiday and dd ended up coming up with us in the middle of the night (couldn't sleep on the floor). Also at this point we decided it was a good opportunity to stop her bedtime milk - she protested the first night for about 10 mins but that was that really(we had wondered if the milk was making her wee more in the night and waking her up - even though she still wears a nappy to bed). When we got back from holiday we put her straight back in our bed (things not set up in her room as we'd used it to dump suitcase etc) but after a couple of days we decided it was time to pick up where we'd left off. This time though we had set up a star chart with a star given for every night she stayed in her own bed (with me sleeping in her room) - of course she had already been doing this prior to holiday but we wanted her to have a sense of achievement. After 6 stars she got a present. Also during this time I began to leave the room before she was asleep ...so, stories, lights off, bedtime song, kiss and cuddle and then I would "sit on my spot" a small circular rug from Ikea. After 30 seconds I would whisper "I'm just going to the loo, I'll be back in a minute" and off I'd go returning within 30 seconds, popping my head in the door and saying "oh I've just got to turn the kitchen light off, I'll be back in a minute" and so on until she was asleep 5-10 mins. The next night I left a longer time beween returns. And so on through the week.
The second week a new star chart and a new challenge - dd to stay in her own bed and me to sleep all night in my bed, dd to try not to call me in the night explaining that the better sleep we have the better fun we can have the next day. First night I was up about 7 times over the space of about an hour and a half, a quick kiss and cuddle, a reminder of the star chart and then back to my own bed. A few hours of uniterupted sleep and then back in again to give her a kiss and cuddle (she never gets out of her bed she just calls!). Second night better with being called about 4 times over the space of an hour and then again a few hours later, each time I went in. The third night called in about 6 times (getting hazy here!) the first time I went in, the second time I called out to her from my door to go back to sleep reminding her that she was sleeping in her bed and I was sleeping in mine - still had to go into her, third time tried that again I got back in bed and she was quiet. 4th time I had to go into her and the next couple of times I just spoke to her from my door. Night before last she called to me about 7 times over and hour and a half, I went into her twice and rest of the time I spoke to her from my door. Last might she woke up at about 2.30, I spoke to her from my door and went back to bed, at 6am she called me again and cheekily (!) I spoke to her from my door and told her it was still night time and to go back to sleep ...she said "ok" and then woke for the day at 7. OMG AMAZING! to be fair though it was her first afternoon back at nursery and then we went to the park so she was probably very worn out. During this time I have continued the gradual withdrawal at betime and for the lasst few nights have given her a kiss and cuddle, and immediately said I'm "just going to whatever and be back in a minute" (have left door open a bit too and she has night light but hall light is off) and then gone off and usually sat here on mumsnet for 15 minutes until I know she's asleep (use baby alarm) and then shut her door (never fully). I'm still expecting to have some rough nights and tonight may not be as great as last night but I really feel like this time, this time we are getting somewhere. I hope so because like you I am so so so tired and my patience is more or less at breaking point.
So, to summarise this is what is working for us (famous last words) 6pm tea, bath (but not always), tv (yes! before bed!), no milk, brush teeth, into bed at about 7.15pm, stories until 7.30pm, lights off, bedtime song, kiss and cuddle, me popping off to the loo or whatever, dd usually asleep by 7.45pm. Sticker chart and making a big thing of a successful night the next morning, not making a big thing of it if not a great night. Explaining to dd every night what is expected to happen and why. Trying to not go in to dd but talking to her from the door but knowing when this isn't going to work and responding to her needs asap to stop her waking up fully and getting distressed.
It has taken us a long time to get there with many ups and downs and trying lots of different things. Who knows it could just be her "time". I'm hoping that things improve to the point of putting her to bed and not seeing her again until morning time unless I sneak in for a little look to watch her sleeping
I really really feel for you, it's a long hard slog. Hope some of this gives you something different to try - good luck in finding he combination of things that work for you and your dc