I used to be a single parent of 3 children with an income of below £30k and a mortgage.
How I managed:
Tax credits to fund childcare/childminder.
Charity shop clothes and toys.
Freecycle for furniture etc
UK based caravan holidays in basic parks, not Centreparcs or abroad or even Butlins.
Penny pinching - would walk to save petrol, buy cheaper cuts of meat or veggie food, supermarket own brand essentials/value food. Would regularly go to supermarket at 5.30pm to fight it out with the other paupers for the yellow sticker produce.
But we always had hot meals, the heating was on, we had days out and some treats so it wasn't miserable. It's just about avoiding unnecessary spending and always choosing a cheaper option.
When I first met DH, he had been used to a high income (his XW was a high earner) and it was a revelation and quite shocking to me as to how he used to spend without thinking or even looking at the price.
I am much more comfortable now financially, mortgage paid off etc and have savings but the feeling of financial insecurity has never really left and I am still inclined to be frugal.