I'm going to butt into this forum where I rarely post.
First, Thumper, you came into this world NAKED, not in a diaper.
Second, I am 100% in favor of people doing whatever they want behind closed doors and out in the open that doesn't harm other people.
Third, contrary to what most people think, a funeral is all about the family, NOT THE DEAD PERSON simply because the dead person is DEAD and knows nothing about what's going on and derives nothing from the pomp and ceremony.
When you're dead, YOU won't know if you're in a suit, burial shroud or a diaper. Your family probably wants to remember you in the best light they can remember you, unless you have a "fuck you" attitude towards them.
I sincerely hope your wishes are kept confidential from anyone who might be embarrassed by your decision. It would be silly to embarrass family members in front of guests who loved and cared for you during your lifetime.
A closed casket (locked shut) is probably in order for you.