Sleep deprivation in the first year is not weakness, and there is no trick that fixes it

Night waking in the first year is ordinary physiology, so sleeping "like before" is off the table for a while. What helps is unglamorous: catch sleep in short pieces during the day, split the nights honestly with the other adult, and let the flat stay messy. Sleep comes before tidiness.

One thing worth separating out: if the exhaustion has turned into constant low mood, anxiety, or numbness towards the baby, that is no longer about sleep.