Son, boxing is either punching with sandbags or boxing. If you just look for a sandbag and use brute force to hit it without formal guidance, it is a trivial matter to do useless work, but it is a big matter to hurt yourself.

Do you know why professional athletes put bandages on their boxers? This is to protect your wrist. The wrong punching posture is the most likely to damage your wrist, and even worse, it will cause a fracture.

If you want to buy something for boxing, I suggest you mix the speedball with the sandbag. You don't need to buy too long sandbags (the long ones are for free fighting practice), but they are heavier.