I'm in a similar boat! I'm 40 now though, and our DD is 10 months. We'll start ttc when she's one, so not long now! 😬
I get 18 weeks full pay on mat leave too, and this time, with annual leave, have managed to take 15 months off my main part-time job, which I go back to in early Sept. But, I've worked since DD was 7 weeks one morning a week in my second job because it's been lucrative enough to make it worthwhile. Is there any way you could set something like that up for yourself? If you take on a second job before week 26 of your pregnancy, you can keep it through mat leave from another job. If you're full time could you condense hours to do it?
I had a planned c-section due to breech and it would have been nice to just relax, but on the whole I think working one day a week was a good move for us. DD's dad took care of her by himself, which grew his confidence and helped them bond. We were so relieved she was ok with expressed milk from a bottle.
In June, DD will go into nursery 3 days per week, and I think we'll try to keep that consistent for her routine (and my sanity) while I'm on mat leave again (finances permitting). We'll probably try to replicate what we did the first time because it worked well, but of course there are so many variables! You mentioned that you have a nursery place, but would a childminder be a cheaper option, until your DC is entitled to free hours? That might enable you to keep them in some childcare at least during mat leave with DC2. Childminders might also be a bit more flexible than nursery with dropping down a day or two, then going back to full time etc.
I'm very nervous about all the things you mention with a second, including navigating a newborn alongside a toddler. But, I really like the idea of getting all the nappies and sleepless nights out of the way. Now DD sleeps through I'm dreading the return to it already!