Same here. It's particularly hard for me to imagine Irish and Australian accents without cringing so hard at how bad it sounds in my head that I just switch back to imagining a British accent. Maybe watching something like Peaky Blinders would help.

One Piece Film Red is great! Not sure how confusing it would be for people who don't watch/read the series, but I loved it even though I'm not caught up and haven't been introduced to half the characters yet. Btw, give One Piece a shot! The series up to episode 325 is on Netflix and the dubbing is top tier imo. Guarantee you won't regret selling you soul to the Straw Hat crew xD