I stopped co-sleeping with DC1 at 2.9 completely. DC had been starting the night in own bed for a long time then coming in when first waking anything from 10pm-3am. I stopped cuddling DC to sleep at the same time which helped.
At bedtime did usual routine then instead of cuddling to sleep said I have to just tidy up and fiddled about refolding all DCs clothes. DC watched and eventually fell asleep. Progressed to having jobs to do in room next door which took a minute then a few minutes etc. If DC shouted me I popped my head round said I was busy but would come back. DC got the hang of it in a couple of weeks.
For night wakings I went in and back rubbed and put sound machine on. Would cuddle sat up but not lay down with DC. Less tears over a couple of weeks.
DC has gone through periods of resisting DH doing bedtime/night wakings. He would come in to listen to the stories, then would read a story, then would be the one who stayed being 'busy' in the next room.
DC now 3.2 went through a good period of sleeping through but now I am pregnant (35 weeks) is waking several nights a week again, usually just once before midnight. DC has become more clingy to me/resistant to DH going in again so he finishes bedtime every night with a song and still goes in for some night wakings. Its improved gradually (a recent bug has not helped!). Wake ups are now a quick hug, reassurance and I leave within minutes. Its helped that DC can tell me why....dreams are usually that I have gone away/been taken away or monsters in the room.
DH started to sing when he settled DC but I dont, its his 'thing'. DC tells me to go away and daddy come and sing which I think also helped him be involved. 90's britpop is apparently good at dispensing with monsters!
For context DC has been on the worst end of sleep since day one. I tried many sleep training methods many times but I wont torture myself with it any more. DC will get there eventually. I understand what PP is saying re few nights crying and it will get better....but the level of that depends on your child. Mine needed reassurance or was awake all night hysterical which was far more tiring. I don't like the phrase 'rod for own back' that's just mum guilt. I expect DCs sleep to deteriorate again when baby arrives as it's an unsettling change. Having DH be able to settle DC really helps me...but I appreciate that might not be possible depending on your circumstances.
I hope things improve for you OP it's hard going.