"Can be aggressive" may refer to either general aggressiveness (especially once they reach sexual maturity) or aggressiveness when spawning.
Many fish can cope with 'standard' water conditions outside their preferred pH as most fish these days are spawned in captivity. Years ago, when the hobby was new, all fish were wild caught and did not cope in other water parameters but these days many will tolerate a reasonable difference.
If you want to breed them it sometimes requires making sure the pH etc are more to their liking.
What is the pH of your tap water? If it is up around 8.0 for instance, you might consider an African set-up but if your tap water is soft and acidic perhaps tetras or discus would be the way to go. It is easier to keep fish according to your tap conditions to start with than to try and fiddle around trying to raise or lower the pH.