Hi,
Your partner is honest, bigger isn't always better. Any boob at all is good. If you want to go a little bigger for extra confidence, it's not impossible, but B cup isn't "measly", it's a goal for a lot of people doing NBE.
All companies do their sizing a bit differently; unfortunately it isn't standardized. Shopping for bras has never been easy even for those with experience. Luckily is has gotten a lot easier with all the resources available today. I wouldn't focus on just the numbers and letters, the cut/shape, the wires (or lack thereof) matter as well.
Two 32B bras, even if made by the same brand/manufacturer, won't always fit the same. A padded 32B and an unpadded 32B wears different, same goes for a wired and unwired bra, wide and narrow cupped bra, and so on. As you can see there are various factors than determine fit other than size.
In your case, it's not unusual that all of those sizes fit. A 32A with shallow cups and a 32AA with deeper cups, despite being a full cup size difference, can also fit the same way provided they hold the same volume. They don't need to be sister sizes. I have about 15 bras in different sizes and brands that fit me as closely to a custom as I will probably ever get. I'm a 28/30 band but can wear a 34, 30 or 28 band, anything from a GG cup to a J depending on what it is. Some give me a fuller look, some give minimized look, yet they all fit like a glove.
If you can't get a live fitting, there's a subreddit that can recommend brands, sizes, as well as offer fit checks if you're unsure if a bra you have is a proper fit for you. Professional bra fitters, average bra wearers, they're all on there including yours truly.
https://www.reddit.com/r/ABraThatFits/wi...ers_guide/
They will likely recommend you find your approximate size first (no one has a "true bra size"). It will give you a place to start. You can find it using a bra size calculator, there are two but I find the second more accurate if you measure correctly
https://www.calculator.net/bra-size-calculator.html
https://www.abrathatfits.org/calculator.php
See what it gives you compared to what you have. If the band gives you support without cutting in/riding up in the back, it is the correct size. The right sized cup size/shape support and comfortably contain all tissue, you should be able to fill out the cups without any gaping or spilling up top and no empty space at the bottom.
Feel free to PM if you need still help.