Wow. Thanks so much for all the great responses.
He sleeps brilliantly from when he goes down at 630pm until around 3am, which is something to be grateful for, I know.
In answer to the questions about how he is running us ragged, he tends to wake each night and have trouble getting back to sleep in his cot.
One night this week, he woke at 3am, I brought him down to the living room in dark and he went back to sleep on me - out cold - but when I tried to put him back in cot, he cried and sat up. So l lay on sofa with him on me and he slept until just after 5am. Sometimes I can sleep like that, sometimes not.
Another night he woke around 3am, DH did same thing and after the cot refusal DS did not want to go back to sleep, waking up properly within about 20 minutes and walking around/playing for the next three hours, despite my DH's coaxing.
I think we are getting up with him far too quickly when he wakes and of course it's disruptive to go downstairs to another room (we need chair in his room I think).
So I tried something new last night for the first time. I put him down in usual way but in early hours when he woke I let him make some noises (there was an initial cry out but not crying) and some babbling and I did not go in. He woke a couple of times doing this and then was back asleep within a few minutes. So we all got a good night's sleep
. Going to try again tonight and hope it's not a fluke.
Obviously, if he is really crying, I will still go in but it has showed me that nothing terrible happens if he squawks a tiny bit and babbles "Mamamamama" and we don't leap to attention. In fact, it seems better when we don't.