I can identify with that worry you mention Lydia
I can also identify with some of the post natal depression you mention too.
I had my husband around to help out when needed.
Getting those routines up and running in the first year, particularly with the first child, I felt helped with keeping everything manageable and having the experience to feel more confident with subsequent children.
If I felt flustered or close to getting overwhelmed, I knew I could have all of the peace and quiet I needed after they’d gone to bed.
An upset or poorly child can emit a lot of noise

I used to focus on solving the problem.
Collecting all of the facts and data and by process of elimination work out what could possibly be the matter and how best to fix it.
(It stopped me focusing on the noise)
I too watched mine like a hawk,
Initially for fear of anything happening to them (I could prevent or be on hand to rectify any issues or problems)
After a while I became more interested in their development and how they learned rather than worry about them dying ‘on my watch’, so to speak.
Watching them like a hawk turned into enjoying observing developments.
It became an interest for me
If ever I felt irritable, close to losing it, I’d strap them into their pram and go outside, marching off up the street quickly.
Rain or shine, day or night.
The motion of the pram, speed walking or change of scenery would help calm me. (And them)