I'm buying things in second hand shops too, cos I don't want to spend loads on clothes that might still become too big. You have to search a bit, but I've just bought some really smart work clothes at our local shop.
Incidentally firespirit, I find looking good in business/smart clothes easier, cos they're made in more substantial fabric rather than from jersey and so on that clings too much to the lumps and bumps! and the shapes sort of skim the bad bits.
Good luck with your new job and all the best with finding clothes.
Jay