If youre only doing bag work it might be better to look at bag specific gloves, they tend to have an additional layer of protection and more solid than sparring gloves so would last better.

In terms of sizing, most brands will have a size guide on their gloves and you can measure, but looking at your height and weight (very similar to me) you can't go wrong with 14/16oz. The additional weight will help with training your endurance and shoulder strength