If you wish a church funeral, ask the advice of the organist at the church, as a minister or priest is entitled to veto anything too worldly. The organist will know what the present incumbent feels about the matter, and even if both the organist and the priest predecease you, or go somewhere else, they are unlikely to have suggested something wildly unsuitable.
Otherwise go down to your local library and get someone to help you find some of the pieces of music suggsted here, either online or on tape or cd, so you can listen to them and make your choice.
My father who was quite unmusical requested J.S. Bach's organ prelude over "Jesus, joy of man's desiring" both for my mother's and his own funerals. I suggested and he approved adding the Scottish metrical version of the 23rd psalm "The Lord is my shepherd" sung to the tune of "Crimond" and "Abide by me" as she had been fond of both, although going on my own preferences I would have preferred the Scottish metrical version of Psalm 121 "I to the hills will lift mine eyes, from whence doth come mine aid".
If you are not planning a religious ceremony I suggest you ask some of the younger members of your family whether there is any piece of music they especially associate with you, then you might want to chose that, on the asssumption that they will be present.
A good friend of mine whose service was in no way religious, had asked for a recording of Edith Piaf singing "Je ne regrette rien" as he liked both her voice and the sentiment.
