Hi Carolyn - one of the founding crew, welcome back!
How is he sleeping in the daytime? Does he have a good pattern? If you're trying different times to go to sleep it might be that a lack of consistency is off-putting for him - difficult, I know, when you're still trying to work out what works best. If you set a time and then stick to it though, he should adjust.
How do you handle it when he does get up early? And also, have you tried a couple of distractions for him in his cot that he can play with for a bit and then maybe go back to sleep again?
Another thing I find helps is the power of suggestion. I know it sounds mad, but when I tell Florian that I'll see him at 7 for milk he usually makes it to within half an hour of that time (if we're at home etc.)
Good to hear from you, hope you like some of the changes we've made in the last year