I want to practice acoustic guitar without disturbing anyone else. I want to be the only person who can hear it. But how can I do that? Would it be okay if I buy an amplifier with a headset? Will this solve my problem?
There are a number of silent guitars on the market. These are quite similar in principle to electric violins - a solid non-resonant body and fitted with piezoelectric pickups at the bridge. In addition headphones and possibly an amplifier will be required for silent practice.
Some are available as nylon-strung versions for classical-style guitar, as well as steel strung.
(Yamaha's range is marketed as the Silent Guitar, but other manufacturers probably make something similar; I'm not making any recommendations.)
The point of an acoustic guitar is that it can be heard without need for any amplification. To have an instrument that cannot be heard by others, a solid guitar is a better option. That can then be connected to a small amp, etc., and headphones. What are the reasons you don't want to be heard? They may give other options.
I think this is a bit of a silly answer, but you could get a cheap/old acoustic guitar and rip the back off. This would kill all the acoustic resonance and you'd get hardly any noise.
But as others have said, an electric guitar is a better option unless you need an acoustic for specific reasons (which you should add to your question). However, even an unplugged electric guitar makes a reasonable amount of noise... not enough to wake your neighbours but enough to be annoying to other people in the same room.
If it is an acoustic guitar then I would suggest that you weave a shoelace or something similar around the strings near the bridge. This should reduce the sound significantly. Another idea is to use a piece of thick paper to strum and pick instead of a plastic pick.