Ciasa
You really have 3 options available to you;
1. Depending on the length of your trip, take your formula with you
2/3. Do it gradually or just change it altogether to all his feeds (as you said in your post)
It really depends on your LO temperament, when I changed from stage 2 to 3 formula, I gave the new one twice a day and the older one twice a day (he only gets 4 bottles).
Are you able to get the 'new' formula in the middle East or where you planning on doing the gradual change in Ireland?
Have a good trip
