as others have said, the bloating subsides. I was definitely bigger at around 6-7 weeks than I am now, and seriously considered getting maternity wear then. Now, you can't tell I'm pregnant. Well, I can, DH can, and my mother can, but that's about it. I was a size 8 pre-pregnancy - at 15w, I'm now a 10, and have put on precisely 500g. I went to Monsoon and bought a few clothes in their sale - a couple of smock-type tops, an empire-line dress, and a knitted skirt with an elasticated waist - all in a dress size 1 bigger than usual. I figure they'll be wearable post-pregnancy too. I'm still wearing pre-pg jeans (though I did have a dodgy few days around the 6w mark when I had to undo them by late afternoon!), but I have ordered some maternity jeans. I think I will need them in a couple of weeks' time, but not before.
I have a couple of empire-line and wrap jersey dresses anyway, and they have been perfect, even in size 8 - but I am just starting to grow out of them. I don't have a bump, but my waist has thickened to the point it's vanished. I took a pic a couple of days ago to post elsewhere on here - you'll see what I mean about not looking pg:
If you can find anything left in the sales, you could stock up on a few basics -you may be able to get some of last summer's clothes, for example. I bought a summer dress from JoJoMamanBebe for £10 - by the time I have a proper bump, it'll be summer anyway! But tbh, if there isn't anything left, you'd be best off waiting for a bit, as by the time you actually fit 'real' maternity clothes, chances are it'll be spring/summer (the mat tops all have a 'pouch' which you really need a decent bump to fill, and the dresses are all longer at the front so that the hem is straight when you have a bump). Until then, go for the looser styles like peasant/smock/tunic type tops, or wrap dresses in stretchy jersey material a size bigger than usual, or the wrap tie skirts, if you can find any. Jeans will probably be the first maternity item you really need, since most non-mat jeans are pretty unforgiving. And as others have said, a cheap pair of trackie bottoms for slobbing out at home will do for evenings/weekends.
Oh - and you'll need to sort out your underwear drawer! You will need non-underwired bras soon, for comfort as much as anything else (later so that you don't damage the ligaments or something - there's a medical reason, anyway!!!) - but don't buy too many. Around 10-12 weeks, you'll prob need a different size, and apparently again around 20-24 weeks (so the fitter told me!). And you may want to buy some bikini-style knickers in a size or 2 bigger than usual - I bought some M&S ones in size 12 - because I really couldn't bear elastic round my middle. UTIs are more common in pregnancy, so unless you're a die-hard fan, it's sensible to avoid G-strings/thongs and to go for cotton underwear, or at least cotton gussets.
gosh, this has turned into an epic. Sorry!