I want a more heart shaped butt - is Aveli and lipo of hips and fat pockets a good option?

Based on what you’ve described, the best way to achieve a more heart-shaped buttock contour is through a combination of liposuction to the back and flanks, along with strategic fat transfer to the buttocks and hips. This approach helps smooth out the square shape and adds subtle projection without creating an overly large look.
Adding Avéli to address cellulite and Renuvion for skin tightening would further refine the results by improving the quality and firmness of the overlying skin. If you wanted to take a more aggressive approach and have an even more improved result, a lower body lift could address not only buttock shape but also skin laxity from your weight loss.
I recommend a consultation with a board-certified plastic surgeon experienced in body contouring after weight loss, so you can develop a surgical plan that matches your goals, recovery time, and budget.