Thanks for all your replies.
The routine you suggested is exactly what we are doing - monitoring his tired signs and putting him down. We have always wrapped DS as when he gets his hands out he wakes himself up.
We have been lent a swing so I'll give it a go.

Today we got 1 hour out of him, then he snuggled into my chest and slept another hour. It is so cute. But I would still like a little time to myself.

Thanks