I had the same problem for many years. My answer, which came too many years late in my life, I was 35, was a breast reduction! I looked so much younger, clothes fit and I lost that matronly look. Full figured is attractive if well proportioned. I too-large bust on a too-short girl made me look fat no matter what I wore.
The suggestion of V-necks is a good one, also the right bra. The underwired, bust reducing stlyles work very well and can reduce the bust size by up to 2 inches.
The breast reduction allowed me to finally purchase and wear bathing suits and to be known for more than just being 'stacked'.
I wish I had done it sooner. I'm in my early 60-s right now, the surgery was 20 years ago and I still have attractive breasts, even at my age.