I don't know if your DH would be up for it, but something that really helps me (because I'm totally a planner too) is to sit down and discuss a "life plan." Get a time to go out to dinner, and seriously like get out a paper and pencil and start talking about your dreams and goals. You can ask him, what are some things that are dreams for him? Travelling to a certain place? Getting a guitar and learning how to play it? Moving? Getting a new car? Etc. etc. You can make timelines of months, years into the future. You can add some of your own, discuss them, make it exciting. You can ask DH, "Do you see us having another child or just staying with one?" Put it in his hands, see what he says. Then you can look at your timeline and see when would be a good time to TTC. Maybe he looks at the timeline and says a year from now. Maybe he says two years. Who knows. And keep that paper you write on, because you can always revisit it.
I love doing that... it's very exciting and it gives you lots of things to look forward to in your head. It is also very bonding, I find. I keeps DH and I on the same page, moving forward together.
Your DH might just be worried that you want to TTC right NOW (well, maybe you do, but sounds like you're willing to be flexible). It might make it easier for him to talk about if you are willing to show that you will wait until the right time.
My DH waffles back and forth all the time about having a third (though so do I!). Some days he says he wants another, some days he says 2 is enough. Depends on the day.