Hello Diego and welcome to our Community!
I'm glad to hear that you're going to visit Ireland soon!
If you're fully vaccinated, you won't need to present a PCR test in order to access the Republic of Ireland, although you'll need to fill in the Passenger Locator Form. You can find more information about travel restrictions in this article of our website.
As for Northern Ireland, if you have been fully vaccinates you must complete a UK Passenger Locator Form on arrival or in the 48 hours before arrival in Northern Ireland. In addition to that, before travelling, you need to book and pay for a day two PCR test to be taken on or before day two following your arrival in Northern Ireland. You can take a look at this page to know more about current regulations for passenger traveling from non-red list countries.
¡Espero que esta información os sirva de ayuda!