If it is a formal letter, it should follow the structure of formal letters.
In what way do you want to vary your letter?
You write to
How to begin the letter
How to end the letter
an unknown firm/person (BE) (AE) Dear Sir/Madam (BE) (AE) Yours faithfully (BE) Dear Sir or Madam (BE) (AE) Yours truly (AE) To whom it may concern (AE) Truly yours (AE) a woman whose name you don't know Dear Madam (BE) (AE) Yours faithfully (BE) Yours truly (AE) Truly yours (AE) a man whose name you don't know Dear Sir (BE) (AE) Yours faithfully (BE) Yours truly (AE) Truly yours (AE) a person whose name you know Dear Mr/Mrs/Ms Fisher (BE) (AE) Yours sincerely (BE) Very truly yours (AE) Sincerely (yours) (AE) a person you know personally Dear Ann/John (BE) (AE) (With) Best wishes (BE) (AE) Yours (BE) Love (BE) All the best (AE) Kindest/Best regards (AE)