When I was single parent struggling, these things also helped:
Having one layer long hair and trimming it myself. There’s an easy way to do it yourself straight and plenty of YouTube videos. I got good enough to add fringe and basic layering!
Only colouring every 6 months, telling a good hairdresser I needed it to look okay and it was quite fun! A kind of early balayage that everyone liked. Not too dramatic. I’d spice it up with a home colouring kit of a gentle low light in between.
Not having a car. Saved so much and walked / cycled everywhere, to work and childcare. Child too on the back. Kept me fit and healthy. It was a pain when it rained and snowed though. Kept weight down too.
Good shoes.
One expensive pair of jeans, not in a sale. Two good jersey dresses in a sale. Everything else can be very cheap.
Eating semi-well, didn’t manage fully-well as I was exhausted in evenings.
Make up can be cheap except foundation which I found was better pricey, but used sparingly with face cream so it lasted a very long time. And having one expensive item, even if it’s 40 quid foundation that you’ve asked people to get for Christmas, that you use regularly can really make you feel a bit pampered as it can be a bit depressing always always scrimping.
Motivation was key, so being out somewhere that you felt good was really good for me.