Good advice here, especially the first post.
You sound like a smart, capable, empathetic woman. You can clearly see the issue is your DH’s mindset/attitude. You’ve tried to change it. You (I regret to say) enable him not changing abit, by him not feeling any consequences of his behaviour (he’s still buying shoes, whilst you aren’t!).
What you want is for him to change his behaviour, but I can’t see that happening. So you either live with it, or step up and put boundaries in place to manage the behaviour. Annoying I know, as you don’t want to do more (nor should you have too), but you can only change your behaviour, not his, so you either do this, learn to live with it with good grace, or leave the situation.
As a way of managing the situation, I suggest having a chat with DH and say you’ve going to stop taking on the mental load of worrying about $, and in order to do so, the best way forward for you both is to have one joint Bills account. So you both have your own personal accounts into which you get paid, and then you both have an auto transfer of your total yearly bills divided by month and split in salary proportion, into this Bills account.
Then you have a second joint account called House, which is 1-2% of your house’s value, again divided by the month. Again you both put in an auto transfer every month from your salaries, in proportion. (As an aside, 1-2% is minimum what is recommended people spend on home upkeep each year. So this is for emergency household work when the boiler/oven breaks, the plumber needs to be called or, hopefully, you planning ahead and using it to replace the oven/washing machine/roof when you know it’s getting old etc).
Then you have a third account called Holidays - same as above. Add up the cost of an average yearly holiday, divide the monthly amount it will cost and transfer that amount over. You can’t take a holiday until you have money in the account to pay for it. If you want a big holiday, you might take a smaller holiday the year before to ‘save’ up in this account for it.
I would also get rid of any credit cards your husband has access too. The reason being, you obviously don’t want to do all this, and then find in 6 months time your DH has continued on and run up a credit card bill.
After that, all your money is your own, in your own personal accounts. You can save and he can spend, it’s your own choice. But the three accounts above are not to be touched except for those things. Make them hard to access the money if you too, as the second and third should only be accessed for long planned purchases anyway.
Personally, I would say you need an Emergency Fund of 3 months expenses first, and forgo the holiday fund (or pay more from your own portions) to fund this. But choice for you.
Finally, you have to stay chill, and enforce it. If he ruins a car seat - then HE replaced it from his momey. If he ruins the computer via shoddy handiwork, HE replaces it. If he buys 8 pairs of shoes and doesn’t like them but won’t return them - it’s his money to waste as he sees fit. Equally - your money is yours to waste as you see fit. (So get your hair done properly!)
You have detached. You are chill. The main accounts are secure, everything else is his problem.
In a perfect world, I’d also suggest 6 month Emergency Fund account, offset against your mortgage, and money into your pensions. But that’s something you can work towards. I think it will be v hard to do the above as it is.