Hi John,
As Eoin said, the linked thread above has plenty of suggestions for public transportation passes.
If you don't feel like purchasing one in particular, I would still suggest getting a
LEAP Card or an
Ilink travel card (for Northern Ireland) during your stay. A LEAP card can be easily topped up through the
LEAP top-up app and fares in cities are usually cheaper and more convenient to use (you just have to tap it when you board the bus or train)
I hope this helps - Please let us know about your itinerary so we can help you better.
Antoine