Your earnings are approx. 1/3 of his.
Therefore, on a very basic level, you should put in approx. 1/3 to the family pot.
(Making up numbers here, but let's say for example):
£600 nursery
£800 mortgage
£300 other misc. home payments
£200 insurances
£150 wifi / phones etc.
total: £2050
So the minimum you need to cover all bills is £2050, but there will obviously be other incidental family costs, like fuel, soft play, swimming - whatever you're doing with your son during the week, groceries, maybe a sneaky takeaway here and there.
Monthly take home:
You - £1680
Him - £4300
One of two ways to spin it (bear in mind my completely made up figures!) - either you both pay in a proportion of your salary to cover the spends, which would be about £680 for you and £1370 for him. That leaves him with a lot more disposable funds than you.
Better would be for you to each keep £1000 of your salary in your accounts as your own spends for the month. The rest goes into a joint account for family spends, that will include all of those incidentals. And you both have a nice amount of 'fun money'. Anything left over in the joint account to be siphoned off into savings.
Of course I'm not taking into consideration things like, he has higher income but also has a David Lloyd membership, or you pay £40 a month for an iPhone. I would consider all those to be family spends if I'm honest but some would put them into the 'fun money' category.
This is how I would do it anyway. Hope that's helpful!