How to get him to stay in cot all night?

My little man has been “sleeping” in his own cot for a few months. All starts off lovely.... he goes to sleep at 8.30 and we go through until about 11/midnight and then he’s up. It potentially can then be every few hours he wakes grizzling. Sometimes his dummy (pacifier to all my American friends) will settle him. Because I’m back at work I do tend to co-sleep with him when the grizzling starts as that the way I know it stops.

I keep getting told I’m creating a rod for my own back, but what else can I do? I’m assuming when he starts walking then he’ll be more tired. Any ideas?