"Thoughtful" does not have a prefix or suffix. It is a standalone word.
The opposite of "thoughtful" with a prefix would be "thoughtless."
Unthoughtful
Thoughtlessness has 2 suffixes-less & - ness.
unthoughtful
people there is no prefix for people
Comparative: more thoughtful Superlative: most thoughtful
The comparative form of "thoughtful" is "more thoughtful," and the superlative form is "most thoughtful."
Demo-, anthropo-
Some people do. But most people give thoughtful answers.
The advantages of thoughtful leadership is that is should allow morale within a team of staff to be high. By being thoughtful in leadership it is possible to take on board suggestions from one's team of staff and keep people happy.
A person who is considerate of other people feelings.