Money advice

I'd say open up savings account and every time you get paid put money you don't NEED into that account and just keep what you need monthly. So bills, groceries etc. That is a good start.

As above and change your spoiling habits to buying second hand things for your son. X

I second Diana. I do something similar. On payday I take out money for bills etc and that goes to our joint account. Then I save x amount and then my whatever is left is what I have for the month. That way I am always saving but I also have money to do things or buy stuff.
Also, sometimes it's just the dopamine from the purchase that you really want. Keep all receipts and return stuff you have changed your mind on. I saw an influencer who will take a photo of something she wants in a shop and search vinted for it to see if it's on there for cheaper - a lot of the time it is!
Finally sell stuff yourself. I use vinted and I keep the money I make in a separate account so I have a little pot in case I want to see/do something.
Once your saving starts adding up that also becomes a bit of a buzz! Look for a savings account with a high interest rate and that you can't make withdrawals from in the first 12 months (this stops you dipping in on a whim unless you REALLLLLLY need it)

As soon as you get paid, put 10% of your salary into savings.