Don't overpack and don't buy specific travel clothes, unless you are a frequent traveller. You will probably wear half of what you packed, this is my experience, and I usually pack only a mid size packing cell per person. We survived 2 weeks sightseeing in Europe with whatever we could fit in our daypacks (30l) as i couldn't face dragging those big wheeled luggages from place to place and on planes, busses, public transport, trains... . They are a nightmare in Europe. I washed the socks and undies every 3 days. Best.decision.ever, even though my husband initially abused me and called me insane. He now knows it better😁 i even caught him bragging about the size of our luggage. Yes, we bought things in the last day, the kids and him ended up with a whole new summer wardrobe as i took advantage of the sales and the shoe prices, but we were planning for it and brought an extra bag for the bounty, but we did not have to carry it from place to place. That would have wrecked our holiday for sure.
Carrying enough tshirts to last for 3 weeks is insane. Please reconsider. Pack the absolute minimum and if you run out or get bored with wearing the same outfit you can buy stuff in Ireland, no?
Maybe watch a few packing videos on youtube focusing on travelling w carry on luggage only, they are great, v inspirational.