Are you familiar with the Pivot and Slide method used on knits? There are several tutorials online and it has been used with success. (I did not come up with this method.) Most of the time you do not need to add length unless you have more than a 2-cup difference from your chosen pattern size. But, I always recommend making a muslin first. You can definitely use the traditional dart method on knits and only make the adjustment to the front too as shown in this tutorial: https://projectorsewing.com/full-bust-adjustment/