Is it possible to go up a size with 19% body fat?

If you are too thin for provide donor fat, then a fat transfer is not an option. Implants would work better.

Dear peachesloveberries,
it is hard to tell for sure without an examination. If you are considering surgery, I would suggest you consult a board-certified plastic surgeon. Only after a thorough examination, you will get more information and recommendations.
Daniel Barrett, MDCertified, American Board of Plastic SurgeryMember, American Society of Plastic SurgeryMember, American Society of Aesthetic Plastic Surgery

Filling the upper pole with fat will not make an appreciable difference in contour. This is because fat grafts do not have the ability to 'push' tissue forward or up, a force known as elastic modulus in the scientific world. Body fat percentage tells me nothing about how much fat can be harvested, filtered, and delivered. Your safest and most effective alternative are highly cohesive silicone gel implants. Todays implants are very durable and do not cause disease. SSBI, aka BII, is not a thing. Surgeons use high resolution ultrasound to monitor breast implant integrity in the office in five minutes, and implants like Sientra have a 5% rupture rate at 10 years, making them extremely durable. Do yourself a favor and get the implants and lift.