I'm a 12/14 and a 32F - and finding clothes to fit is a pain in the backside, pregnant or not :(.
For bras, I'm a fan of Rigby and Peller - over the years I've been round M&S, JL, House of Fraser, etc, but R&P are the only ones that have reliably turned me out in a bra that feels comfortable and makes me feel as though I look good. Shame about the price tag on some of their items (they're not all horrendous!) - but I justify it as its an item of clothing I wear all day, every day that has a huge impact on how everything else fits on top.
Unfortunately their maternity range doesn't look so great. I've heard good things about Bravissimo, and I've also used Ample Bosom and FigLeaves before.
For clothes, I tend to resort to tops that have raglan sleeves - that way I can get away with a slightly larger size to get the fullness over the bust without looking like I've pulled a sack over my head. But it does limit options - especially when even tank tops gape around the armhole. Bravissimo have a range of clothing that takes bust size into account, but they don't seem to do maternity (did you know, most ready-to-wear stuff is designed assuming women have a B-Cup? No wonder its a struggle to find stuff that fits! - no use now, but my be handy in a year or so 
). A lot of my maternity stuff has come from H&M at various points in time - should survive at least one pregnancy, and doesn't cost a fortune. I also got a few bits from JoJo Maman Bebe and 1 top from Mamas and Papas. M&S usually do 2-packs of vests that are non-maternity but quite long, very stretchy and don't cost the earth - I found them handy to have for when cold or have a neck line/bra conflict (if that worries you)
Sorry I haven't got anything more definite or positive for you - but I'll watch with interest to see if anyone else has any suggestions. good luck :)