How could I convince my wife to have a baby? Should I get someone else pregnant?

My wife and I have been together for approximately 8 years and have a son who will be 6 years old this month. She just finished her bachelor's degree but is leaning towards getting a master's. I just want her to take some time off so we could work on another child. She says she's not ready and wants to make 70,000 a year. I think that we're doing just fine with our combined salary. She also says that she prefers to travel instead of investing money in diapers. How could I convince her to give me another child? Should I impregnate someone else?