Thanks so much for being a part of this community.
First off, wow, 70 pounds is no joke. That's amazing.
Second. . . you're not going to love my answer but hear me out.
Breast lift and Breast Augmentation are different operations that are commonly done together. They are done together specifically because the limitations of one and the strengths of the other match up. Meaning that an augmentation makes the breast larger and can create shape in the upper and central breast in a way that a lift just can't. Similarly, a lift reshapes and repositions the breast is a way that an implant simply couldn't.
A very simple way to think of it is this:
If you only want to change the size of your breast and the shape of the upper breast, an implant can do those things.
If you want to change the position or shape of the lower half of the breast, a lift can do those things.
If you want both things to occur, both surgeries are probably needed.
Similarly, because the implant is limited in what it can do, it can overcome size differences in terms of volume in a bra, but it's not great at changing the appearance of the larger or smaller breast enough to where the shape is likely to be similar. I can't say without our spending time together, but my guess is not just that you would need a lift for better symmetry but also that you are much more likely to be happy with your results if you do get a lift.
Have a great day,