The scar pattern of a breast lift and a breast reduction are the same. The difference is how the underlying breast tissue is manipulated. In breast reduction the breast tissue is removed while maintaining an aesthetic shape to the breast. Removing both skin and breast tissue allows for appropriate tension to be placed on the skin and minimizing poor scarring. Trying to tighten skin around a 40 G size breast doesn't make much sense to me. The skin has stretched because it can not accomodate the weight of your breasts. I would also think with 40 G breasts you have some issues with shoulder grooving, neck pain and possibly rashes under the breasts. These issues would not be corrected with a lift.
Also the size of the breast doesn't dictate how effective you will be at breast feeding. Often very large breasts make it more difficult for the infant to nurse.
Any surgical procedure on the breast has the potential to diminsh your ability to breast feed. That being said, I have breast augmentation and reduction patients who have been able to breast feed after surgery.