I wouldn't change countries for "just a few days". We love both countries, although Ireland may eek out a win. Both have been largely terraformed by sheep and shipbuilding, so the scenery is quite similar, the whisky/whiskey are vaguely similar, and both have a strong music tradition. There are of course major other differences!
Between Google MAPS, "Things to do" and "nearby Hotels", travel planning is not that hard. I've executed five 3 week trips to Ireland (and four to Scotland) with great pleasure. I have our sixth(2027) all booked, and a seventh sketched out (likewise for Scotland). There are also lots of great websites for both countries (these forums, Irish Road Trip, Hidden Scotland, TripAdvisor etc.) and lots of Youtube adventures. I am retired, so it's far more fun than doom scrolling or playing computer solitaire!
We do an annual trip to either Ireland or Scotland in May (or thereabouts). We do May because I believe the weather is best and crowds are manageable, and we live in fire country and travel later in the summer is a risk. We've always arranged our own itinerary, booked our own lodging, and planned our own stops, and never took an organized tour until our 2026 trip, which had two day tours. We always have a rental car except in the big cities. We also lean towards shorter stays (many one-night and few three night) which is an unpopular style on these forums. We like to get home slightly exhausted. I also start booking things as soon as airline reservations are available (330 days before travel) so I can get extra legroom in economy. I always have several plans in the planning stage at once, and most itineraries are revised scores of times before pushing the button. I currently have a 2030 Scotland trip roughed out. Our 2028 trip is matured enough to book if it was possible.