Ooh - was in a very similar position to you and feel like I have resolved my issues after a couple of shopping sprees.
I popped into Gap and their Maternity range is quite good at the mo - some nice shorts, just above the knee, slightly turned up. Denim, but they manage to tread the line between smart and casual quite well.
They also had some nice basic vests and other lovely looking tops. Also some lovely gladiator-lite sandals, which, whilst not strictly a maternity outfit, have livened things up a bit.
There's a 30% off voucher on Martin's Money Tips (??) at the mo, but it expires on Thursday
I have a pair of hareem trousers from Topshop, which have already been worth their weight in gold. Very loose and comfy, but still quite stylish. I got them BNWT on e-bay and haven't seen them in-store. I also have some maternity indigo Baxters, which look nice slightly turned up as a 7/8 kind of look.
I also bought a lovely dress from Jojomamanbebe [http://www.jojomamanbebe.co.uk/detailfash.php?type=FASH&code=A9971&proddesc=Striped+Boat+Neck+Dress &supercategory=BRN00038&branch=&wcategory=CAT00222&catdesc=&super=0010BRN00038~0020BRN00040~0040CAT0 0222&treecode=TRE00009 looks much nicer on than in the pic].
The bits from last time that are still coming in useful are a pair of 7 for all Mankind jeans (comfortable and stylish, but v. pricey) and some linen trousers from New Look.