Curved vs Straight

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I have my nipples pierced with a curved barbell and I was thinking about finally changing out my jewelry to one of the shield jewelry, but I don't want to irritate my nipples by switching from curved to straight. If I was to switch, would it cause any major problems? Please help! Also, my nipples are kind of on the smaller side and are originally flat. So I don't know if switching to straight would be better or worse.

This is what I want to get.