I'm pregnant and as such my bra size has increased to about a 42F however I'm having trouble finding any bras! I could probably wear a 40G but given that I still have 15 weeks or so to go I'd rather get a 42.
I bought a nursing bra by Royce today in John Lewis. I was advised to buy it tight-ish round the back as apparently my ribcage will go in a bit, and big-ish in the cups. I have 14 weeks left myself. They go up to a 40K and you could always add trt one on with a back extender for a bit more comfort. Online here but better to go instore and try on if possible.
OK, on that basis I don't think a 42F will have quite enough space for you. At the moment, I'd normally suggest trying a 40GG/h and 42G/GG. Normally you buy the bra so it fits well on the loosest hook, but this stage of pregnancy is one of the rare times to buy it to fit on the tightest hook (so you have some room to loosen it off) so I would say the 42s are probably a better bet in general.
I have a feeling that the Royce linked above is known to run big if you are looking for a nursing bra (although you may find a bra bought now won't be the right size for nursing as you'll go down in the band (probbaly back to a 3*) and up in the cup. HotMilk also do up to a 42H, as do elomi