Four dead plants in a north facing flat — what actually survives me and what am I doing wrong?

Buy the lamp. I am in a north facing flat too and the difference between a windowsill with no direct sun and the same windowsill with a decent bulb on a timer for ten hours a day is the difference between plants surviving and plants growing. It does not need to be an expensive panel; a proper grow bulb in a normal lamp on a cheap plug timer transformed mine. The plants that were merely hanging on started putting out new leaves within a month.

Politely disagreeing with the buy-easier-plants advice you keep being given, because most of the lists are dishonest. 'Low light tolerant' means it will survive without dying, not that it will grow, and a lot of those lists include plants that genuinely need a bright room. Sansevieria, ZZ and aspidistra actually will sit in a dim corner for years. Almost everything else on those lists slowly declines and you get blamed for it.

Switch to terracotta for anything you are worried about overwatering. Porous pot, water evaporates through the walls, mix dries faster, and the margin for error on a heavy-handed waterer roughly doubles. It is the cheapest fix on this whole list and it saved my pothos from me.

The Sunday schedule is what killed them, not the flat. Plants in low light use water slowly, so a weekly pour means the mix never dries and the roots suffocate, which shows up exactly as yellowing from the bottom up over a month. Stop watering by calendar and start watering by weight — lift the pot when you have just watered, lift it again a week later, and you will feel the difference immediately. Once you water only when it is light, half the species people call difficult become easy.