You can do that without YNAB though mammy. It's a spender or saver mindset.
I just use a spreadsheet and CBA detailed entering of expenses etc, but I just think about purchases as I go along - will I use this item, do I need it, can I reuse something I already have, have I found the best price, is there cashback or a discount code I can use.
OP have a look at the budgeting section of moneysavingexpert. They have a step by step guide to maximising your income and cutting back expenses such as gas and electric, mobile phones, TV/broadband, insurances etc etc. A bit off each can add up to a large amount overall.
Always think of the total cost of something, not the one off or monthly cost - saving £10 a month off your mobile phone bill might not sound like it is worth the effort, but that is £240 over the typical 2 year contract.
The main thing is that you account for regular annual expenses and things described as 'unexpected' like broken washing machines, car repairs, vet bills etc. These are not unexpected. If you have a car, pet or house, you will need to spend money on it sooner or later. So put money away for these expenses before spending on discretionary things.
Also consider how much you spend on daily incidental expenses like food and drink outside the house, magazines, toiletries/cosmetics etc etc.
If you are spending a lot on these, there can be scope to cut down massively. £2.50 a day on coffee might not sound much, but that's about £600 a year if you do it every working day. A daily premade Pret type lunch each day could add up to over £1k per year.
Look at your supermarket shopping and see if you can use cheaper supermarkets, and use up what's in your cupboards and freezer if you have excess food hanging around.