I would recommend doing some research; both online and in person at various sex toy stores.

There are a wide variety of types of harnesses and it's best to check them all out and decide what would be most appropriate for the type of use you and and your partner are planning.

One website that has a large selection of harnesses to choose from is Babeland. They also have a lot of helpful advice to help you choose one that will work best for you and your partner.