I’m going to ship some books and personal belongings back home soon.
Can I basically go to any post office and they have the boxes there and I use ground (slow) mail?
It would be nice to buy some boxes at the post office to take back to my apartment and to pack the items into the boxes at my apartment.
I also wonder about the cost.
Thanks!
Yes, they do offer this service.
Box prices as below
Size(cm) Price(NT$)
L 39×32×43 45
M 29×21×32 30
S 23×16×18 20
Bon voyage
Because of Covid postal connections with various countries are on hold. So really depends on your destination
I always sent non time urgent items home by ship mail surface. It’s super cheap and will get there in about 3 months so if you’re not in a major rush. They didn’t offer me tracking but the box eventually arrived.
And yes they will give you the box to go but I like sealing it at the post office as they give you unlimited tape.
Unless the ship’s name is Ever Given 
Nice 
The ships name is also kind of ironic since the buyers of the goods won’t be given anything, ever.
Have you considered scanning them and emailing back home? Works out much cheaper.
I use this approach when transfering money between my home country and Taiwan.