Farmers always are their own boss unless someone else owns the land
The most natural way to be your own boss is farming. While the job is demanding and requires extensive knowledge about nature - farming also is rewarding if you engage in non-cattle farming. Farming without any animals - just fruits, vegetable, etc gives you full freedom in life.
What ever job you select to be your own boss, you have to realize that being your own boss also means getting up earlier and working longer without overtime, without paid vacation or other social benefits. Being your own boss means exactly you get what you give. You earn what you work for - nothing more and nothing less. Hence being your own boss may result in having a far more stricter boss than during any employment situation before.
Early in my life I started to be my own boss for most of my life with a few exceptions only. I definitely have been kicking my own butts far more intense and far more often in any single day than all combined "bosses" ever in my entire life. To succeed in your own business requires perseverance and consistence focus on your goals and on the most loving means to acquire your goals. A life without goals may fail - a goal without love to achieve will fail as well. It is the combination of aiming at your goals in a most loving way that creates the basis of true and lasting success.
It is totally unimportant how big the project you have achieved by the end of your days on earth. But it definitely is important how loving you have been all the time while working toward achieving your goals!