I am a veteran of CC and I'm sorry but it works.
(When I say I'm a veteran It sounds like it doesnt work but that's because against my better judgement I sometimes allow things to slip and bfeed to sleep, then have to do CC again)
DD1 was trained at the age of 3 m (dons hard hat) and we had only a handful of broken nights in her entire babyhood. At 4.6 yo she still sleeps well and is happy and well-adjusted.
DD2 is made of sterner stuff and I am softer than I used to be. At 19 mo she still wakes us regularly during the wee hours. Her favourite trick is to stay awake for the next 3 hours while using us as a trampoline. I am still bfeeding her at bedtime and sometimes first thing in the morning after DP has brought her through to our bed. The problem is keeping her awake till I've finished reading DD1 a bedtime story as she invariably falls asleep on the breast.
Anyway, after a particularly gruelling week last week I Put My Foot Down.
Night 1: She cried for about 40 minutes. I went in every 2 or 3 minutes kissed her and laid her back down in her cot. She didn't wake us during the night.
Night 2: She cried for 3 seconds and then went to sleep.
Night 3: She fell asleep on the breast before I put her in the cot but didn't wake till 1am, 5 minutes after I'd gone to bed. I got up and laid her back down. I had to go back in about 7 or 8 times at 2 minute intervals. The last time she stopped crying very suddenly, gave a little cough and went back to sleep.
I am almost hoping she'll wake tonight so I can consolidate the good work!
You need to sleep and your ds needs his.
Be kind but firm.