Or you could go down to your nearest recycling centre where there will be loads of cardboard boxes to choses from.
Once you have your box you then need to measure
Lenth
Width
Hight
and weight.
When you have that info and the post code you want to send to, you can use these 2 site's to get a price. (should be around £15-£20) for uk mainland
You can wait at home for courier to collect or drop of at a parcel shop near you.
https://www.parcel2go.com/
https://www.parcelhero.com/
Hope this helps
Samurai..