Just an update on this.... last night DS self settled - TWICE! And then again this morning.

He slept all the way through to 10 minutes before his next feed and was half awake when we put him down.

At 12:30am he took 20 minutes to fall asleep. In that time, he cried out on 4 seperate occassions, each for 5-10 seconds each and then he would quietened down again. We decided to just let him go and see what happens. He ended up sleeping all the way till 3:30am.
At 4:30am he took 10 minutes to fall asleep - same as before, but he only cried out twice. He slept all the way till 7am.
At 8am daddy put him into bed fully awake, so just lied in his cradle for about an hour, looking around. Then he slept till 11am!!

Changes we made:

- Sleeping bag - we had him in a long sleeve suit, plus a sleeping bag, and 2 light blankets
- Soft Blankets under bed sheet - in order to create more of a nest for him, we put some blankets under his sheet so he sunk into them a little, but not enough to risk suffocation
- Heat Pack - before I put him into his cradle at 8pm, I put a heat pack in there for a little

I'm not sure which of these worked, but I dont really care... he finally got to sleep in his cradle and we didnt have to wake up and hold him or co-sleep once through the night.

Fingers crossed it wasnt a one off!!

Thank you for all the advice ladies - it really helped to get me to open my mind to new ideas and trial and error.