Keep the blue-and-white foundation and tune the outfit for your pace, the weather and how much character detail you want.
For a long day out
Choose the striped shirt and white trousers if you want a relaxed outfit with room to move. Wear comfortable shoes you have already broken in, and carry a neutral bag that leaves your hands free. If you choose the dress, take the cardigan along as a light layer and use familiar walking shoes instead of prioritizing a particular shoe style.
For cooler weather
The Oxford under the ivory sweater vest is an easy layered option. Add a plain navy or charcoal jacket over it when needed, leaving the blue collar visible. For the dress, use opaque tights and a neutral coat you already own; the blue dress and white layer will remain the clearest colors. Keep the black headband or dark shoes as the small contrasting details.
For a quieter reference
Leave off the padded headband and use the dress’s original tie-neck detail with a white cardigan. Or wear a plain blue Oxford with white or stone trousers and no themed accessories. The goal is a useful blue-and-white outfit that suggests the character through color rather than a literal costume piece.