Hi all, thanks got your replies, they're very much appreciated. Just a quick update. After another horrendous night last week DH and I agreed we needed to take action and start being consistent in getting DS to sleep in his cot so that hopefully when he woke in the night he'd be more likely to settle again without needing to be held. I spoke to various friends IRL who had done sleep training and followed their instructions. I was also reassured by my lovely gentle DM that she'd had to resort to sleep training with me as a toddler and I can't even remember it!
We started on night 1 by getting DS ready for bed as per our usual routine, but instead of holding him till he fell asleep I put him straight in his cot, hugged him and told him I loved him very much but it was time to sleep and I would just be in the next room but would come back in 3 mins to give him a goodnight kiss in 3 if he still needed me (if he was crying). I then lay him down and left. As expected he stood up and started to cry which was heart breaking. I set the timer for 3 mins and then went back in to kiss him as promised and repeated the same set of words and left for 5 mins, then 7 mins, then 9 mins, then 10 mins. By the time we got to 7 mins there were patches where he did stop crying and the crying he was doing was less intense. I then did another 10 mins and on that visit he just accepted me lying him down, took his dummy and went to sleep! So that was 44 mins in total.
He woke crying at 3am that night so we repeated the process and that time he decided to accept lying down and went back to sleep after we got to the first 10 min interval, so he was asleep in 34 mins total. He also stopped crying quite a few times during the process and his crying was much less intense. He then slept till 8am and I actually had to wake him up for the day!!
On the second night we repeated the process and to our utter amazement he accept me lying him down and went to sleep after the 5 min interval, so he was asleep within 8 mins!!! Even more amazingly he then slept through till 7.30am!!!!
On the third night (tonight) I thought perhaps last night was a fluke and prepared for a difficult time, but this time he accepted me lying him down after the 3 min interval, but did get up and grizzle a bit again but then lay down and went to sleep after the 5 min interval, so again he was asleep in 8 mins. It's 11pm here and he's sleeping soundly, fingers crossed for another good night.
He's been in a lovely mood these last few days, probably due to having proper sleep for the first time in a month, and we've also felt much better for the sleep and so have had a great family weekend together. I know sleep training doesn't work for everyone but it does seem to have really worked for us, touch wood!