I am definitely not trying to discourage you, but I'll share with you why my family will not be having a third child any maybe it might give you a little perspective.
We currently have one child and another on the way. They will be almost 3 years apart - the spacing that I wanted, although I recognize and respect that for some families closer or farther works.
Our house has 3 bedrooms. If we were to add a third within the next four years, that means we have to move to a larger and likely more expensive home. We're floating along financial street rather comfortably right now, I enjoy that money isn't a stressor, but I have a hard time imagining that the housing market will recover by the time we'd want to be moving. We love our current home and are not looking to 'downgrade', and I'm not quite sure we would be able to move into what we want. Throw on top of that the possibility that our oldest child would be in the 2nd or 3rd grade and I really do not want to have him to switch schools and academically/socially start all over.
Also, once all is said and done with my two children, I will have spent 6 years of my life changing diapers. While I fully expected that task and will happily complete that task, I'm not entirely certain that I want to spend nearly a DECADE taking care of small children. I'm a little apprehensive about going through sleep training yet again with this new baby, but knowing that it'll be my last time I can deal with it just fine.
Age is a big factor for my husband and I. While we're not *that* old (35 when this next baby will be born), it just isn't for me to be having more kids around the age of 38/39. While some people are fine with having kids later in life or they had to have them later in life due to some necessity, it's just not something I'm willing to entertain. Pregnancies are not the 'glowing joy' for me like they are for many people; there are many complications I have to deal with that make them almost seem like 9-month medical issues. I just don't think that, for me, it is smart to demand that of my body again.
Career-wise it is also tough. During my 'childbearing years' I am sort of stuck in my position with no chance of advancement while I take FMLA time to adjust to being a new parent. Long-term projects, getting involved in yearly committees - well, that gets really tough when I know I'm going to be taking 6-12 weeks of leave and then knowing that I'm also going to be responsible for picking up my kids from daycare in the evening. Working extra hours or overtime is not an option. Not that my career is more important that my children, but it just becomes difficult to balance the two and I cannot imagine extending my 'limbo' for another several years.
And finally, the money. I would NEVER have kids if I didn't think I could afford them (again, just how I feel; I know others feel differently). Having kids requires spending money on diapers, formula or BF supplies, clothing, doctor visits, child care (if parents work outside the home), and then as they grow older - private school tuition perhaps, sports/activity fees, and the list goes on and on. I know these expenses exist and my husband and I anticipated them. We wanted to make sure that we would be able to give our children every opportunity available - not spoil them and give them everything they want, but not grow up in a household where we are scrimping, pinching, and stressing to make ends meet. I never want to wonder how we're going to make the house payment or wonder how much debt we can run up on the credit card because we can't pay our bills every month. I want my children to see two hard-working parents who are responsible with their money, can live within their means with limits, yet able to provide a comfortable lifestyle. In our family, in my opinion, I think this would push us to our financial limits. And, when families suffer financially, they tend to also be stressed out and children notice that (boy did *I* notice that with my parents...they were always stressed out about money and although they never came right out and said it, money was the huge elephant in the room).
So, as you can see, for us there are several reasons to NOT have a third child. Many of those reasons are very personal and possibly unique to our situation. Again, I'm not discouraging you but just sharing my perspective into our decision-making as to why we are not going to pursue a third.
It's good that you and your partner are discussing this. Maybe set aside some time to really do a "for once and for all" objective conversation where both parties list pros/cons and try to come to a decision. Best wishes to you and your family!