Personally id just modify bras that i liked into nursing bras. Bravissimo has some of the largest sizes available (however the two i own have the firmest wires ever!) I had my kids well before abtf during my 20yrs of stuffing my boobs into 34dd/ddd bali granny bras. I bought a 36J royce nursing bra and it was too small by those standards even. If i had to guess i was probably a 32M I was literally double the volume i have now at 28J/30HH
Ewa (and i believe comexim?) make nursing bras too.
If you are not handy with a needle and thread you can have a shop like nordstoms or local bra specialty shop modify them. I think someone asked and nordstroms charges 15 bucks to modify.
I would suggest a bra with stretch lace such as the andorra or jasmine if you stay in that size range. They will accodate a larger fluctuation of size. When you are nursing, esp early on your cup size will vary by several cups.
My oldest (now 11) i called my "boobshark" because that kid would still be on my nipple 24-7 if i let him. Hes clingy. Lol. I would nurse him in the am before work (around 6m old) and pump around 14oz off the other boob. My cupsize probably varied by 4 or more from am to post feeding. I nursed him til just shy of 2. He slowly weaned himself. From 18-24m i dont think my cup size changed much at all.
My second nurseling (now 8) wasnt nearly as big of a fan. I pushed him to nurse about 14m before i stopped pushing him. My cupsize didnt fluctuate as much because he ate just enough to take edge off hunger and went on his own merry way. Hes super independant and would get mad when id cuddle him! I had problems pumping more than 15oz at work when with my oldest i would pump 50oz at work. Initially my boobs were huge and engorged until my supply adjusted to my 2nds demand. So my boobs didnt fluctuate as much.
But either way stretch lace will help adjust a few cupsizes. You wont know how much until your supply/demand is established ;)
Since i had horrific bras i lived in a built in cami tank (maternity) with a prefold tucked inside until i had to leave the house. And i became queen of sliding bra straps off shoulders in public under my shirts. Lol. I can sew fairly well but i didnt bother since bras fit so poorly. Wish i had found bigger bras back then!