Need help replacing a toilet flush valve and install new unit

I need a reliable handyman to replace our toilet's flush valve and install a new compatible unit. The bathroom is on the first floor, and there is easy access to the cistern. Please include removal of the old valve, installation of the new kit, and any necessary sealant or fittings. I’d prefer a quiet, punctual plumber (Gas Safe not required for this task) who can verify there are no leaks after completion and provide a brief brief explanation of the work done. If you can suggest a good, standard replacement model, that would be helpful. Access is straightforward, and I can be flexible with the start time within 9:00–17:00 on weekdays.