My first bra was a 36A (but because I listened to the 'add four inches to your band' advice I should have been a 32C. I went up to a 32D a year in, and now at a Victoria's Secret or La Senza I will normally take a 32G (but normally 34DDD is what I have to settle for). My most recent purchase at Change Lingerie was a lightly lined in 32I, but this is still less than my 36K mother. Due to the shallowness of my breasts, and of most trans women, I visually look like a typical D, so make sure to get measured in a proper boutique!