Short answer: Some people can handle a low-intensity psilocybin experience alone, but solo tripping raises the chance of panic, confusion, or unsafe choices. If there is any chance the experience will be strong, having a sober sitter is recommended.
Choose a sitter if it is your first time, you plan a medium or high intensity experience, you have had challenging trips before, you are in an unfamiliar or outdoor setting, it is at night, or you feel emotionally unsettled. A good sitter stays sober, calm, and focused on safety.
If you still go solo, keep it as low-intensity as possible, prepare a safe and quiet setting, remove hazards, avoid mixing substances, have water and simple grounding tools ready, tell a trusted person your plan, keep help reachable, and know your local laws.
If you want structured support, consider hiring a professional trip sitter; you can explore what that service involves at this page.
Stay safe and be mindful.