Weeelll. I know EXACTLY where you're coming from. So, what I did was I bought a pair of "booty shorts" bathing suit bottoms, and a bathing suit tank top (mixed and matched, besides, I'm all different proportions). It made me feel a little more comfortable about my thighs. And when I'm really in a weird day, I'll put a pair of my old sweatshorts on. They're kind of fitnessy looking, and oddly they look good on me. Booty shorts also hide my stretch marks on my thighs
I would say instead of stepping in to the old bathing suit, if you're really dreading it, why not consider buying a new one? You've come SOOO FAR!! in your weight loss, and you deserve it!