I usually just use my sparring gloves for sparring and nothing else.

ten ounce or 12 ounce gloves should protect you hands well enough for hard bag work as long as they are of reasonable quality.

To respect your training partner's safety you should keep your sparring gloves in the best condition possible.

The padding in sparring and competition gloves is usually different to that in bag gloves - it will wair out faster but be safer for your opponents in the meantime.

If you like to work with extra weight on your hands for your bag work you can get weighted gloves you put on under your bag gloves. Also hitting a heavier bag will be harder work than hitting a lighter bag power wise.

If your hands are injured easily from using the bag gloves look into getting better ones