Hi there, I exclusively breastfed and co-slept and by the 8.5 months I was a Zombie but I didn't want to try controlled crying.
I stumbled upon Baby Whisperer methods which is a variation of controlled crying, the difference is the baby is crying on your shoulder so they don't feel abandoned. They cry out of frustration until they learn to self sooth. I think this method is good from 4 months, Baby Whisperer has different methods for different ages. Unfortunately, she passed away age 54, her books could do with some refinement. Baby Whisperer Solves All Your problems is the best, here is her method.
You put your baby down they start to cry. You wait until they become hysterical and pick them up. If they stop crying on the way to your shoulder- you picked up too soon. You calm them down on your shoulder then put them down. They start crying on the way down- you still put them down and wait for a hysterical note. Repeat. The idea is to ignore the cries of frustration and only pick up on cries on distress. It does take a lot of resolve
The first time I tried it took 1.5 hours. I thought my baby would never forgive me.. He woke up all smiles and actually was less grumpy since we mastered this method. I think he was chronically overtired just as I was (used to wake up 8-12 times over the night).
Baby Wisperer used to work as a neonatal nurse, she knows a lot about babies and young children and there are lots of good tips in her book. Ignore her breastfeeding advice, times were different, the rest of her book is excellent. She literally saved me from a nervous breakdown. I continued to breastfeed till 13 months.
Baby Wisperer also says day and night sleep are related, overtired babies don't sleep well at night. She suggests following the baby's body language rather than the clock. Main sign of tiredness at this stage is yawning if I remember it correctly.
This is the time to use pick up/put down technique. I vaguely remember her saying 1.5 hour naps are better than 45 minutes ones, corresponds with my experience. As I have said Baby Wisperer used to work as a paediatric nurse with babies and young children. I swear by her advice. I used her other technique with my other child- he was doing 5-6 hours at 2 months whist being exclusively breastfed and despite being a much more difficult baby to start with.
She has written quite a bit on broken trust for people who had tried and abandoned controlled crying, especially if it was done when babies were very young. She says her methods would still work, however might take longer. I can't remember the specific tips, it might be worth getthing the book of Amazon. Second edition with yellow cover is the one I would recommend..
If you really can't stand the idea of letting your baby cry you can try No Cry Sleep Solutions by Elizabeth Pantley. I hope it helps