I've done runs from Dublin a good few times in the past (between IKEA when it was only in Belfast, Sainsbury's in the previous recession (DD in nappies then), learned about Banbridge for clothes, and the odd weekend in Belfast as a family.
Newry is only about 90 minutes from South Dublin, maybe 2 hr at most. (I travel to Cork frequently so find even as far as Belfast is grand). Banbridge is literally only a few minutes further for clothes. Or sometimes going on as far as Lisburn for an M&S outlet, Toys'R'Us and another big Sainsbos; or Boucher Road (Lakeland!!! Chain Reaction for DH bike stuff, and I know there were afew more there).
Newry has a few decent shops in the centre with Sainsbos (including a Superdrug), and there's a second SC across the road. There used to also be a big ONeills shop in the car park for sports gear. A very easy spin off the motorway on the southern end of Newry, down to the bottom of the hill and turn right into Sainsbos centre.
I found Banbridge very good for clothes for me - if you know Kildare Village, it's quite similar. But there's no supermarket (as far as I can remember) so I would go there first and then Sainsbos in Newry on the way home.
Lisburn is really not that much further north though - another 20 minutes? I got good value in toys there some years, and a few things that Smyths/Banba etc didn't seem to have down here. And with the Sainsbos there, I didn't have to stop on the way back either.
There are some lovely craft shops in Belfast (I know I found 2 great ones and can't remember their names, but they were city centre).