How much money do you need for mat leave / a baby?

I’m still pregnant but just working out a budget and I realised I don’t know many parents who had children in the last 5 years or so, so here I am online!

I currently spend around £3500 a month on rent, bills, food and activities / random shopping.
I don’t live with my boyfriend (yet) so this is just on myself.

I’m self-employed and therefore won’t qualify for enhanced maternity leaves or anything like it. I do plan to slowly pick up work and do as much as I can maybe around 4-6 months postpartum, I’m not sure yet.

Boyfriends on a higher salary than I am, will obviously be contributing (significantly) to everything but I don’t want to only rely on him either as I feel that’s not fair.

Excluding rent/household bills as I know there’s no one answer, what is a good amount to put aside to use as spending money for when you have a baby? How much did you spent monthly on your baby and yourself during maternity leave?

I’m a bit worried not earning much for this long!
I was out of work for 6 months before a few years back and it was not good financially.