I will literally be doing this tomorrow.

You can get moving boxes at Jumbo, rated for various kg amounts. Once I talked the handle holes shut, the Post said they would be acceptable.

Since you're taking the handle holes shut, I found the 25 kg boxes to be ideal.

You'll have to bring them to the Post.

There are way bills on the Post website

https://www.mypostbusiness.ch/portal/?login&lang=en

Actually post.ch/frachtbrief is probably better

25 kg to Ireland is around 80 chf with economy shipping.

https://www.post.ch/en/post-startsei...iness-zone.pdf

https://www.post.ch/en/post-startsei...rtcut_info-int


Just ask for the post package service to Ireland, they can give you the right brochure and highlight all the critical bits