I'm definitely the maternal type but am happy with our DD. Even if we'd been able to conceive her naturally and easily, it still wouldn't make any difference to how I (we) feel.
Just because I love kids and always have, doesn't mean I want a tribe of them around me Everyone's different though. Other posters have given great advice, but I think if you and your DP are going to continue to "butt heads" so to speak, about this issue, a professional "referee" in the form of a counsellor is probably what's going to be needed.
I think I'd be saying to my DP if I were in your shoes that "right at this very moment in time, I do not want another child and can't see myself ever wanting another child as I'm happy with things as they are. However, I'm willing to revisit the issue with you in 6 months/12 months time (agree on a timeframe together) and we can go from there. Until then, I don't want to talk about it at all etc as all it does it make me feel pressured etc".
If you feel differently after that time, that's great, but if you still feel the same way, then you and in particular, he, is going to have to find a way to learn to accept that's how you feel. What anyone else thinks/feels/says is totally irrelevant IMO as it's a personal decision between you and your DP.
1 child families are becoming more and more common for many reasons in this day and age. The way you raise your child is what shapes them, not whether they have siblings or not!!
Having another child because you think you should or you feel pressured to from your DP/family/friends etc is going to be far more detrimental to you, the relationship between you and your partner and your current child then choosing not to IMO.
I wish you and your family the very best of luck with this