Bird of Paradise do very well in hydroponics. Transferring them can be a challenge - but it's definitely worth the effort.
Pot size depends on the size of the plant. I always suggest a hydro pot the same size or even slightly smaller. Keep plant on the dry side while it is adapting. That means pouring water through the pebbles until it runs out the bottom - then stop. Repeat once a week for 4-6 weeks.
The challenge is these plants are usually pretty big and which means they need a lot of moisture to keep growing. That's difficult for new roots.
Warm temperatures at the roots (75 degrees or more) is critical for new root growth. That can be difficult in the winter. Also, dry air found in most homes adds to the situation. I suggest waiting until spring for repotting.