We discovered a few things with DC2 but they are partly due to us being in a house with stairs rather than a flat (as we were with DC1) and having a car.
Changing caddy in the living room with wipes, nappies and changes of clothes in to minimise trips up and down stairs.
Changing mat in the living room.
As many things to plonk baby in or on as possible - we had the crib upstairs, Moses basket downstairs, bouncy chair, and now can use the Jumperoo and a doughnut cushion.
We bought new spoons and sippy cups for weaning, a new mattress for the crib, an Isofix car seat base (easier than belting in a second seat - I found this really fiddly for some reason) and a Moses basket.
Shnuggle bath is amazing!
We also needed some new clothes, mainly seasonal (eg summer rompers as DC1 wasn’t in them at the same age).
DC1 decided he wasn’t bothered about the buggy board but with your age gap I think you’d need that or a double.