You've gotten a lot of good advice & insight. The one thing I would add is that you should consider the hormones you would have to take for IVF. When we were trying to get pregnant, we had decided that we wouldn't go any further than the IUI procedure, mainly because of me. I am a pharmacist, and I just had... still have... concerns about what those hormones may do to you long term. There is still much that is unknown since, relatively speaking, this is a recent (30 years or so) procedure. If you are happy with your one child, then consider how much you want to put your body through and whether it's worth the toll. My sister went through it, and I saw firsthand the ups & downs and the emotional aspect of it. I, personally, didn't want that. Fortunately, we did get pregnant, on our own, just before the first appt with the fertility doctor.
We tried for a second child, it didn't happen, and we decided that was God's way of telling us that one child was the right decision for us, for now, though we may someday adopt (biologically we are done).
Good luck with whatever your decision.