I speak as a friend of someone who boxes, so don't take my word as the ultimate say. That said, I did find a good resource on boxing gloves.
For size, the recommendation is based on body weight:
- 120 lb and down: 12 or 14 oz
- 120-150 lb: 14 to 16 oz
- 150-180 lb: 16 to 20 oz
- 180 lb and up: anything 18 oz or heavier
If you are pursuing boxing, stick with boxing gloves. You can get some training gloves for the heavy bag and keep a pair of sparring gloves for matches. The resource I linked to is precisely for this target audience and it's more specific recommendations on glove types are great for boxers. Always get hand wraps when you wear heavy gloves. Hand wraps prevent your wrist from bending, which is a higher risk when you have weighted gloves.
However, if you are pursuing general martial arts, you just want a pair of bag gloves. Bag gloves just keep the canvas of the bag from chewing up your knuckles and don't provide much protection. However, they do allow you to practice your strikes much the same way as they would in a street fight. Hand wraps are not necessary for this option as long as you have proper technique (i.e. no bends in the wrist). This last bit of advice contradicts the article, but the article was written for boxers, not more traditional martial artists (i.e. karate, tang soo do, etc).
If the heavy bag is for martial arts conditioning, then I recommend just keep doing what you are doing. Striking with boxing gloves and as close to bare knuckle fists as you can are completely different disciplines. I have a martial arts background, and I've used the heavy bag for power and conditioning work. If you have a good striking technique, then just use it. A couple of tips when working with power on the bag:
- Time your punches. The bag will swing away from you, and when if you punch while it is traveling toward you, it will put more strain on your wrist than is necessary.
- Crowd the bag, reset, and repeat. You are going to attack the bag like you would an opponent. When the bag swings away, close the distance and follow up with more punches.
- Practice footwork and approach. A particularly useful technique to help with sparring is to practice your footwork and combinations from different distances. Timing is important in sparring, so this will help you work so that it's more effortless.
The only thing that working with a heavy bag requires is that you keep a tight fist and your keep your wrist straight. If you don't feel like you can do that without help, just get the hand wraps as training wheels. If you relax your fist, your whole hand will collapse on contact. The force of clenching your fist also radiates the power up your arm, reinforcing the wrist joint. You should be able to draw a straight line from your first two knuckles and your elbow. Any up or down bend in the wrist puts your wrist at risk for a sprain or break (depending on if the bag is swinging toward you and how quick your reactions are to pull your punch if it doesn't land right).
