Old Navy Secret-Slim Underwire Plus-Size One-Piece Swimsuit There's extra support thanks to the wire in this Old Navy Secret-Slim Underwire Plus-Size One-Piece Swimsuit ($50-$57, originally $57), coming in solid black or a zebra pattern. Image Source: oldnavy.gap.com Old Navy Secret-Slim Underwire Plus-Size One-Piece Swimsuit $50 from oldnavy.gap.com Buy Now