You could go through the sewers, that's supposed to be the "pure" playthrough path to the city, and is certainly harder. Though afaik the enemies there, if you can't avoid them, give at least +1 corruption per fight, unless you use a spell that requires having completed Mountainreach, which itself is mana-intensive and challenging. And if you enter the city that way, that means no drugs and no spell.
Viewing post in Getting into the demon worshipper city (balancing?)
0 trust drugs are possible. Low trust just means 'Mary' can't 'exit' the city through the sewer entrance and can't 'enter' the city through the basement. That does not mean the inverse is true. Aura just needs to talk with Liliana to unlock the disguise, use the sewer entrance once to discover it, exit, and go back in. The teleport beacon also allows you to be in disguise. Spells do have trust requirements though.
The corruption condition is not having a nearby lightsource. Radiance turns Aura into a lightsource but casting fire on nearby torches also works.