3 pots. Survive, spend, save.
Either get yourself a bank any with virtual pots within one account, or open 3 seperate accounts.
On payday, or the very earliest opportunity move the required amount of money for monthly bills/childcare/subscriptions etc into 'Survive' account. All done and dusted, no need to worry, that will take care of itself, assuming you're accurate in knowing how much you'll need.
Move enough money into your Savings account to cover 1/12th of your holiday, Christmas fund, car tax, etc, basically everything you pay for once a year. You have to do this at the START of your month, not just what you have left over, else you won't be putting enough away.
Figure out how much you typically spend in a week on costa, magazines, greggs, cinema, pub lunches, make up, etc and times by 4.3 (ish) to give yourself a monthly figure. If you're shit at keeping to a budget you might want a 4th account to feed yourself one weekly allocation at a time. Keeping to weekly "pocket money" will get rid of the status quo where you're just tapping your contactless card and it's just coming out of one massive bottomless pit of salary (which does have an end!).
It sounds so simple but so many people don't do it. If I just had one account for everything I'd always be short like you've found yourself. 15 years ago I did it by drawing all my 'pocket money' out at the beginning of each month, and sealing each week into brown envelopes labelled with each Friday in the month. Now banks allow 'pots' it's a whole lot easier!!