The standard harness is designed for a body that's shoulders and hips are wider than the waist. Of course bodies come in all shapes and sizes. If your waist is larger than your hips, the force of an upside down fall may cause you to slip out. If this is the case, you'll need to look into a chest harness. If you plan to climb during the winter with additional clothing layers, you'll need a harness that will adjust for clothes.
Harnesses offer few options.
Some have a Velcro and buckle closing. Easy to use, but can also be easy to forget to fully secure the closing. A harness should have gear loops for attaching climbing equipment. These are typically designed for carrying lead climbing gear. Gear loops are not designed to take any pressure.