If you don't mind having your good healthy teeth on either side of the missing tooth number 13 ground down, then a bridge would be the next best alternative. In the 21st century, however, a fixed bridge is a compromised treatment, and implants are more like replacing a natural tooth. You will have to floss under your bridge and clean differently than you would an implant. Cleaning an implant tooth is more like cleaning your natural tooth, and it does not require for you to have natural healthy tooth structure taken away. Removable partial dentures or another option but it would be extremely inadvisable in your situation to just replace one tooth with something removed both. And unilateral partial would be a choking hazard, and a full partial denture going to the right side for stability would be way too much removable hardware. Cleaning it would be very difficult which could lead to tooth decay due to food entrapment. Patients with removable partial dentures usually do not like the way they feel or look and end up putting them in there drawer instead of wearing them in their mouth.