I would like to...

Become immortal (but without immunity to diseases and other ailments)

so that you die of cancer, HIV infections, the flu, and other nonsense.

Be rich (but without the ability to leave your home)

so that you become the most successful among prison inmates and go crazy from being confined.

Fly into space and not return

so that you die from a lack of oxygen, food, water, warmth, and other joys of earthly life.

End up in a fantasy world

so that you die at the hands of the first bandits you encounter or end up in anal slavery and die an even more agonizing death.

Gain one superpower (you can't upgrade the first option, nor any others)

so that you are treated like a laboratory rat, and in the end, they kill you in order to study your brain.

Turn into a specific person (without the wealth of that person)

so that you feel inadequate and continue to envy that specific person, or suffer from those who envy and dislike that person.

Acquire something real but unattainable in this life (we're talking about something that can't be bought)

so that you get a useless, worthless thing that won't affect your life in any way.