We each have individual accounts and one joint account. Both salaries are paid to the joint account which pays for everything household and children related and our individual accounts are for our pocket money. We take the same amount each week and do what we like with it. OP, if you're both getting paid into individual accounts, can you keep back the same as your wife gets paid and whatever is leftover can go to the joint account to cover everything else.
For example, let's say your wife gets paid €1,000 per month and you get €4,000. You keep back €1,000 like she does and transfer €3,000 to the joint account. If there's not enough there to cover everything then you jointly make up the shortfall. Seems the fairest way?