My mum is like this. And I learnt from her as a child and have been inclined to this previously.
I've found getting into budgeting helps, with a specific aim in sight for what I'm saving for. So for example I've saved to go travelling years ago (when I hardly learnt anything!) and have more recently saved for holidays and a deposit to buy a flat.
I now have direct debits for my essentials each month (rent, bills phone etc). I then put a chunk is savings and give myself a reasonable set budget for each month for "spending money". This covers eating out, food & anything else like clothes, house items etc. I put this on a pre loaded Monzo card with the idea that when this is gone that's it & I have no more spending money until the next payday.
I then question the spend when I'm considering making a purchase on my Monzo card:
Do I NEED this?
Will I actually use it?
Is it worth it?
Is it good quality/will it last or is it a false economy?
Do I really like/need the item or do I just think it's a bargain?
Can I get it for less elsewhere?
(Obviously I don't question every single food item I buy but having these kind of questions in mind does stop me bulk buying things like chocolate and crisps!)
If it's a big item I'll consider if I have to make cuts from my budget to buy it or if it's worth putting it on my credit card to pay off on payday.
I'm pretty sure there's a list like this on Martin Lewis' Money Saving Expert website so have a look on there for tips.
Ultimately it's a whole change of attitude. You have to want to change your habits and stick to it. I still splurge a bit on clothes every now and again, but I find myself really thinking about what I've already got which is similar, and I tend to buy a few better quality things which will last rather than a tonne of stuff from Primark!
I find this works for me. Not everyone is the same but hopefully you'll find it useful food for thought.
Good luck!