Personally, I am still lifting heavy and trying to grow boobs at the same time. My upper chest is still quite a bit bigger than across my nipples, which does quite a bit to hide breast growth. I have adjusted my workouts to target only the lower chest ( such as declined bench press ). If you want your breasts less noticeable, target the upper chest.
I have also stopped doing isolation exercises (such as bicep curls), and mainly work on compound exercises with more reps, plus more aerobic exercise ( currently running 2-3 miles a night). Doing this gives less of a defined look, but you still keep most of your size and strength. My arms are still almost 20" around the bicep, but don't look nearly as defined/muscular as they did a year ago.