Actually getting a proper handle on my finances has been the single thing I did last year which has contributed most to my general mental wellbeing. Historically I've been terrible at it, I'm paid incredibly well compared to most of the population, but because I wasn't consciously budgeting I'd end up running down to the last few pounds in my bank account every month.

Putting an effort into setting actual budgets at the start of the month means I'm shifted from impulse buying silly things on the basis that I have the money at the moment to holding off on those and saving some money. (And admittedly still making silly impulse purchases, but with solid data that I can afford to do so and still have enough money left over for food).

I can highly recommend the ridiculously named You Need A Budget (https://www.youneedabudget.com/) if you're not sure what you're doing, since they have a ton of content around how to go about budgeting. Even if you don't buy the software, give their educational material a read.