We are doing similar intenerary (miami to Buenos Aires). Discuss with your doctor as the medical recommendations can be affected by your age and other risks. Wife and I are both over age 62 and doctor proceeded as follows for us : no yellow fever vaccine recommended , anti- malaria pills ( there is no “vaccine”) taken before, during and after being in the risk areas, and hepatitis a and b vaccine . Note that the combined a/b vaccine may be hard to find and may be hard to schedule if you are close to sailing. It involves an initial shot, followed by another a month later and another one down the road for maximum effectiveness. That said, my wifes Dr said some protection is better than none!
also check each country you are stopping on the state dept website ( link in the Oceania notice) as some have YF vaccination requirements that are not the clearest and not sure if “enforced”. Worst case is ,I assume, you won’t be allowed off ship if not vaccinated.