Many of the women's BC's should fit you as they are made shorter than the unisex (men's) BC's. You would just have to try them on as they each seem to fit different body types.
Personally, I would instead suggest a short backplate and wing, as others have mentioned. It is infinitely adjustable and an exact fit to your body whether you gain weight or lose weight. I find the 30 lb Halcyon Eclipse wing to be too long and it attaches way too high on the small bp for a very short person with a shorter torso, causing the wing to protrude above the neck/head even if the bp is placed as low as possible. (I suggested years ago to Halcyon that they consider multiple attachment points and/or a shorter wing, and they said they would consider that, but there's nothing yet).
Deep Sea Supply has a slightly shorter bp than the Halcyon and UTD makes a shorter bp/w for people 4'11 and up. Either would fit a petite person well.
I found the switch to a bp/w no issue at all without any training, which is really not necessary. My LDS adjusted it to me and then I adjusted it more very easily later. I tried one in the pool first and it felt just like diving with my women's bc.
Good luck!