I still do it now on the odd nights our 2 yr old wants to stay up.
It's so difficult but it has to be done.
I know it's even harder the younger the little one is because instincts tell us to run to our children when they're crying.
Our 5 month old is a very light sleeper so although he doesn't cry - in the sense of wanting to stay up, we still have to let him know we're there but don't take him out of his cot or talk to him unless there's something wrong.
With our daughter, the only way it works is to do the whole routine of bed but as soon as she's 'supposed' to go to sleep, it's lights out (blackout curtains have helped a great deal)and make sure she's comfortable etc. then no more talking. If she gets up I'll go over and lie her back down - again no talking.
The reality is - most nights it works but it's so difficult to do on an emotional level.
You just have to remember that as long as they're crying for attention and not because they're in pain or frightened, then it's ok to continue with controlled crying.
Have you tried dream feeding? Expressing is a great idea, at least you'll know how much he's taking to ensure he's not hungry. Also, instead of giving up on breast feeding, you could always give him a night feed of formua.
Napping - Could you pop him into the pram and go for a walk each day for a week or so at a specific time to encourage him to sleep? Then hopefully, after a week or two he'll have some sort of day time routine for sleeping.
- even if it means letting him sleep in the pram in the house for a while then move him to his cot.
Fingers crossed it'll all come together soon.