Hi L.,
As you stated, when, or even if, to have a second child is a personal choice and involves alot of factors; including, relationship, health, finances and the type of relationship you want to have with each child and the type of relationship you want them to have with each other.
Naturally, there are some things that are out of our control such as the sex of a baby, or the person who wants two children very close together who ends up pregnant with twins on her second pregnacy. (not everything can be planned!) You also haven't mentioned how your husband feels about adding another child.
I can tell you from my experience: I have four children. My first two were with my first husband and they were almost seven years apart. Although, I got the pleasure of nurturing and focusing on each child as a baby, my children who are now 29 and 23 were not that close growing up and my eldest who is a girl frequently expressed resentment towards her younger brother. They are now 29 and 23 and quite close!
My first husband died quite young and I remarried when my son was 12 and my daughter was 19. I have two little girls with my second husband who are 21 months apart and let me tell you. IT IS ALOT MORE WORK! Not just because I am older, because I actually think that helps. (more patience, more insight on the passage of time, more ability to appreciate all the joys of motherhood) Two babies are simply alot of physical work. I frequently felt like an outsider on their relationship who was in charge of the clean up!....lol.
It's not to say I am not close to my young daughters, because I am, and we try to find time for one to one interaction. But, the gift they have of each other is a great one. Now that I see two very close siblings, I couldn't imagine one without the other. It is just different. Now that they are getting older it is getting easier (ages 7 and 9) but still challenging at times. (one child has no one to fight with!)
Well, I'm not sure I've helped with your decision, but I would try to be sure your relationship can withstand the rigors of the physical effects of pregnancy, the financial pressures if you can't work etc. before making the decision. At ages 30 and 42 you both have time.
Best Wishes and God Bless,
J. L.