I'm 39, with 2 daughters aged 10 & 12. My sister is 37 with no children and has been umming and ahhing for the last 3 years about whether or not to have a baby with her partner. We have talked at length about it (as I'm sure you can imagine!), but what it really came down to in the end was that she just wasn't sure, so they have decided they won't be having children.
I think that's the best choice if you're not sure - obviously you can't really change your mind once they arrive, and it's not even as if you can take a holiday from being a parent when it all gets a bit much. If you went through a particularly stressful and busy period at work, you might decide to take a break afterwards; have 2 weeks laying on the beach in the sun to relax and unwind. Once you've got children, you don't have that option. Yes, you might have amazing (and rich!) Parents, who see that your toddler has entered the 'Terrible Twos' and has been giving you the run-around for the last few months and think you could use a break, so offer to care for your DC for 2 weeks and pay for you and DH to holiday in the Maldives, but whilst you're paddling in the crystal clear waters, the heat of the sun warming your skin and a Strawberry Daiquiri in your hand - you're still a Mummy. You'll still worry if you packed their favourite teddy, worry if your Parents are following their bedtime routine, that your DC might fall off the climbing frame at the park and end up with a broken arm (or worse). Basically, 'Mum Guilt' is real, and it's with you all the time.
You can never really relax, even when you're away from them - what if they were injured and you needed to get to them in a hurry and you were at a meeting 250 miles away? Even sharing a bottle of wine with DH on a Saturday night is a risk; what if DC fell ill and needed to go to the out of hours Dr, or to A&E - someone needs to be sober enough to drive (yes, I have heard of taxis, but there's often a long wait at the weekend and we all know how MN feels about calling an ambulance in non-life-threatening situations!) You are always a Mum first, before you are anything else, because that's how our brains are wired.
Having a baby is the one choice that women make in their lives which limits nearly all the other choices she will ever make in the future.
I'm not trying to put you off, just present you with the realities of how it affects women (me and all the Mums I know, at least!) and share with you one of the main deciding factors in my sister's decision not to have a baby.
I, on the other-hand, have always wanted to have children - not that I thought about it a lot particularly, but I just assumed that I would be a Mum one day. Then, when I was 26, a couple of friends and colleagues had babies and then I did start thinking about it a lot! Here we are 12 years later with two wonderful, clever, kind, well-mannered daughters of whom we are incredibly proud. For me and DH, having them is the best thing we've ever done, and it's brought us closer together, as cliché as that all is! I'd personally recommend Motherhood - but it's not for everyone!
You know that only you and your DH can make this decision. If you're really undecided, why not push him a little more on whether he would like to go for it or not. He has first-hand experience so knows the realities of it all, so who better to ask?
Good luck in coming to a decision, I'm sure you'll make the one that's right for you.