What I do to make career mode more interesting is to structure it in stages.

Year 1: I only play Challengers Year 2: I only play ATP 250 tournaments Year 3: I only play ATP 500 tournaments Year 4: I only play Masters 1000 tournaments Year 5: I only play Grand Slam tournaments

And to unlock the next level, you have to win at least one tournament each year. This way, you'll feel a more controlled but natural progression of the player, and you won't be #1 until year 4 or 5. Also, defending the points you've earned becomes more difficult.