It turns out that you can acquire the first game’s original costume very early in the game! Just chapter 2 and it’s even story-based, i.e., impossible to miss. I thought I had to work for it, lol.
As for whether Caster’s bust size has increased from the previous game, it remains to be seen, but maybe it’s just the second costume. They could’ve just simply reused the sprites and 3D model from the first game instead of fixing them a little bit to be consistent, lol.
The second costume kinda grew on me, though, even though the first costume is still the classic one. I would probably use the first costume for one chapter and then revert back to the second costume, just for nostalgia (and since I no longer have the first game). I don’t mind change and generally prefer to use original costumes of respective games. Case in point: I don’t even revert Wright to his classic costume in Ace Attorney 5.
This tendency to stick with original costumes is also why I don’t particularly get a kick out of Project Diva modules or Tekken customization or fighting game color palettes etc either. Hypothetically speaking, if I were to play League of Legends, I wouldn’t buy any skin either. I just stick with the original costumes lol.