Assassin Coming After a PC

I'm hoping to tie in a PC's backstory by having an assassin from the Crown try to kill her after word gets out of where she's located. They will be level 6 (DnD 5e) at the time, so I'm looking for advice of a good assassin stat block to use, any minions/henchmen that might realistically be involved, and any tips for setting up the moment when they have to confront the assassin.

I have a plan for making them paranoid (mistaken identity and a food mix-up results in someone else dying when it was intended for the PC) and have them start connecting the dots before the confrontation with the assassin.

Any advice would be welcome!