When you book flights, be sure the name on your ticket is an exact match with what appears on your passport (i.e., use “Thomas” instead of “Tom). Some airlines may deny boarding if the name on your ticket doesn’t match your passport.
Finally, if you don’t like your assigned seat, find a better one. Most airline websites permit you to move your seat, provided that it's within the cabin where you’re booked. I prefer a window seat distant from restrooms. My favorites are bulkhead and exit row seats that have more space.