Venus's direction is irrelevant to surgery, unless you're having surgery on a body part ruled by Venus, or Venus is the chart ruler for the time of the operation. Breasts are ruled by Moon and the sign of Cancer. Moon cannot go retrograde, so you're safe on that count.
For Venus to be the chart ruler, Libra or Taurus would have to be rising at the moment the surgery begins. You didn't include the scheduled time of your surgery, so I can't say whether it is or not, but when the sun is in Capricorn, your surgery would have to start in the middle of the night to get Libra rising. For Taurus rising, it would have to be in the mid-late afternoon. If your surgery is scheduled for the early morning, as scheduled surgeries usually are, a Venus ruled ascendant is impossible at this time of year.
For breast surgery, the important piece is that you don't want the Moon in Cancer, because when Moon is in the sign that rules the body part being operated on, that intensifies it, and raises the risk of slow healing or further problems. On January 6th, Moon will be in Pisces. Again, you're fine.
It's also considered best to have a waning Moon if the surgery is to remove something and a waxing Moon if the surgery is to add something. Moon will be waxing on the date of your surgery. If you're having a breast augmentation, that's the ideal phase. If it's a breast reduction or a mastectomy, not ideal, but not the end of the world either. My mom had major surgery (removal of a kidney) a couple of months ago when the moon was waxing, and she recovered just fine. Mars was retrograde, too, which is supposed to be the other no-no for surgery.
You won't get an ideal chart for surgery, ever, so don't worry about it, especially if this is a medically necessary operation. If it's medically necessary, you don't have the luxury of being picky. If it's elective surgery, you may have some wiggle room, but still, you'll never get a perfect chart. If this operation is already scheduled, don't go to the trouble of changing it just because of an astrological chart. It may be as close to perfect as you're going to get.