Cotton on has been my saviour for tops. They are stretchy, you can layer them, they have thick straps so bras arent a problem and they are only $10.

As for pants, i have a few elastic waisted skirts that were already in my wardrobe and i have a pair of cargo's from P/patch and some jeans from there also. I think it is worth investing in the basics as you are probably going to be wearing them for about 1 year all up - unless you are lucky and fit back in your small clothes earlier.