modest formal wears for lds and mormon

Can any one lend me an 'evening/formal dress for Saturday Evening? I need something for a works awards ceremony in a Manchester Hotel, so must be smart, elegant, tasteful? modest formal wears for lds and mormon
Size 18/20 depending on design? Have LOADS of shoes to choose from so open to all colours/ styles? Be SO grateful of a loan rather than have to go shopping at last minute ?