If anyone has one joint account with their SO, and both have separate accounts as well... I need advice

Me and my partner are thinking about keeping our separate accounts but also getting our first joint account as well strictly for savings. He’s horrible at saving money so this is the best solution. However he makes way more money than me so I’m wondering how we can make this fair

For anyone who has done this or does this, how much do each of you put in the joint savings a month? How did you decide fairly based on each other’s incomes? How much money would you want there to be combined by the end of the year?