I absolutely adore
Lucy, and it doesn't need to be short for any other name. That said, if you want to use a longer full name, you are spoilt for choice.
Lucia is stunning, but the down side is that there are three different ways to pronounce the name, which can cause confusion.
Lucinda,
Lucilla and
Lucille are all beautiful, or
Lucienne,
Lucretia,
Lucine,
Lucette,
Lucetta, etc, if you want to go with a more unusual choice.
Lucie, the French spelling, is a stylish alternative to
Lucy. To me, the name
Lucy is classic, and I can imagine it on a girl or woman of any age, in any profession or life circumstance.