Perhaps the shift from one child to two was what made it difficult last time?
If you are learning towards non-termination perhaps you could come up with a plan that pinpoints all the previous difficulties and try and put in place things to prevent the same problems occurring.
Your 4 year old will be in full time reception, yes? That will remove some of the pressure from your day, one less child at home during the school day. And no childcare fees (excluiding after school care if that is necessary).
Is there a possibility of keeping the 2 year old in nursery while you are on leave, to ease your burden? This will allow you to nap etc during the day.
Do you have the space for an au pair perhaps to help with childcare, chores, or just a mothers help? Maybe advertise for a regular babysitter/mothers help, perhaps a childcare/ teaching student?
Do you have a regular date night now that you can keep going?
Do you both have equal child-free leisure time? Do you have the chance to have a weekend away alone?
Other timesaving strategies. Cleaner? Shopping delivered?
Maybe you can look at the fact that at least this time you are aware of the pressures that you may face and can prepare for that in advance. Something that you may have not been aware of last time. That is a big advantage to have.