Yes if you're overweight and obese and need to book two airplane seats for yourself you can do so.
Just book the two seats at the time you book your first seat and you'll pay the same price as one seat but have to pay for two seats on the airplane.
Airlines do know that some people who are obese and overweight fly with them and need to have a second seat so that they fit properly on the airplane seat.
You just pay for two tickets like you would pay for two passengers and then you have the seat next to you available for yourself.
If you're not obese then it may be hard to book two seats for yourself to keep others away because airlines need to get as many passengers on the airplane as possible.