If you go with lighter gloves for the bag, the extra weight will make you feel slow when it's time to spar, so for that reason I recommend 16 oz again. If you ever compete (in boxing or mma) your hands will feel like super fast because of the smaller glove weight used in competitions.
A lot of people go with 14 oz for the bag and mits, dunno why. If you go smaller than that, it doesn't protect your hand as much so you might have to dial down the power on the heavy bag.
Some people like tiny gloves (bag gloves) for the heavy bag so they can get a feel for punching accurately with the right part of the fist, etc. You can definitely "feel" it more through the glove and that includes pain if you do something wrong.
I was blasting the heavy bag with these 16 0z. They dont feel heavy at all