First of all, the most convenient way is to buy it directly at school. Generally, when freshmen start school, there will be an area in the school that specializes in selling daily necessities such as bedding and mats, and there will be notices. It is very convenient to buy it and take it back to the dormitory directly. But the quality is not necessarily the best.
If you are not at ease, you can buy it and send it to you directly, so that the quality of the cotton core inside can be guaranteed to some extent.
You can also buy it online, remember to give it some time in advance, otherwise the delivery may be slow. Take a blanket first, at least find someone you can trust, or you might as well go to school.