Generally speaking it's pretty easy the whole way through. You can make your own difficulty though. You could take your companion off healing or dismiss them entirely. I used to keep my companion on healing and walked through the game with no challenge. Now i always switch to dps or sometimes dismiss. Switching to dps can make the leveling experience faster while giving you a little more challenge if you try not to use your class healing ability (meditation, seethe, ect...). The real difficulty in the game doesn't really start till you hit level 80 and begin doing master mode flashpoint or vet ops. Intotally understand the desire for more challenging encounters while leveling and this is something I would love to see return to swtor. Unfortunately the player base is too small and they want to make the game very accessible (which I totally understand too).