Contrary to what people may have believed, this achievement is actually acquired by reaching the "Painter" or "Wife/Child" ending, whether that's your first, second, or twenty-ninth playthrough (because the painter literally makes up his mind about what he wants). The "Wife" ending, being the neutral ending, is the easiest to get and will not get you this achievement, hence why people may be confused.
The "Painter" ending is probably the easiest of the two required endings so here's some tips on what I did to reach that ending:
-Avoid the wife at ALL costs (don't go towards the arch of chairs, turn back when encountering her in the dark tunnel, don't peek in the paint-filled room she's in, pull the elevator handle left when there's a choice, don't turn back when it tells you, turn back when in the yellow corridor after the room starts burning, don't search around in the dark after dropping through the door on the floor)
-When given the choice of going through either the door with the melted wheelchair on the right or the door with paintings on the left, go through the door on the left
-When given the choice of going through the light-filled door after the daughter makes a noise or the door blocked by paintings that the rat goes down, follow the rat to the painting door
-When in the room with the dark pit and crank, ignore it and carry on going
In regards to collectibles, this was the run where I went and found EVERY SINGLE rat drawing, word item and memento for those achievements. They may have counteracted each other as I still got the "selfish" items, so to be safe, go for only items related to the painter and NOT the wife/child if you aren't grabbing everything. This means alcohol bottles, glasses, rat drawings etc. The painting only becomes a self portrait at the very end of the game, so don't worry if it still looks like the wife near the end.
I haven't achieved the wife/child ending yet so I'll try and update with tips regarding that one when I have it.