How to Help my Fat Survive After a BBL?

The best way by far is not to put any pressure on the fat—so no sitting for a minimum of two weeks. Eat a good diet, exercise early but gently after surgery, and wear a well fitted compression garment.
When you start to sit do it for very,very short periods of time with very frequent breasts to relieve the pressure on the newly taken fat cells. So stress the fat by sitting on it and cut off it’s oxygen,and then stand up and let the fat cells breath. I This way the fat cells will get stronger and you won’t run the risk of killing some of the new fat cells that are still very delicate.

BBL outcomes are entirely dependent upon graft viability and survival. The greater the survival, the more successful the outcome. These grafts are very pressure sensitive as pressure decreases local blood flow which then potentially compromises the graft take.
The recommendations for prolonged sitting/unrelieved pressure will vary from one physician to another. I generally recommend avoiding prolonged sitting for a month or so. Occasional rest periods for sitting using a specialized pillow with escalating frequency and length are progressively integrated as a patient heals.
A traditional desk job should be avoided for at least a few weeks. A specialized pressure relief pillow is an absolute. I recommend patients work towards 1 hour total of seated resting per day by the 4 week mark.
As always, discuss your concerns with your board certified plastic surgeon (ABPS). 

Thank you for question. Every surgeon has a different recovery protocol so it is best to talk with your plastic surgeon about what he/she recommends for you. With that said, I advise my patients not to sit on their rear ends at all for the first week. After then they may sit for short periods of time with a pillow under your legs above the knee for 8weeks and some patients use a special BBL pillow to alleviate pressure on the buttocks. I would not recommend sitting normally without a pillow for 8 weeks. Good luck!