Lisalou, I know that lots of folks will have advice for you on this. I also know that there are lots of us who have been in exactly your situation recently. I'll be interested to read what has worked for others. For me, I found what worked was a very limited wardrobe of mid-end items and a few low-end. H&M trousers happen to fit my body shape very well, so I bought a pair or two of those. I also bought several of the Gap work trousers that were wool blends but washable. They weren't as structured or quite as good of quality as I usually bought, but at $40 or under when on sale (which you can often catch them at), they were a good value. I found that a couple of pairs of neutral pants (black and gray ones for me) were invaluable. I also really found skirts a much better value than trousers. I bought them tighter and they would sit higher on my waist. As I lost weight, they sat lower on my waist, but they fit for much longer than my trousers did.
I'm guessing most of us will need more details to give you good advice. How dressy/casual is your workplace? How much do you have to spend on your wardrobe pieces? Are you set up with good basics that still work for you? How comfortable are you with wearing the same thing over and over for a while?
I felt like I needed at least four bottoms that fit me plus a pair of jeans for casual Friday and weekends and a larger mix of tops. My pre-pregnancy tops fit me a lot earlier than my bottoms, so I focused on bottoms. I also had a lot of good accessories (purses, shoes and scarves) to help me add variety to my small wardrobe. I was perfectly happy to wear my cardigans and jackets open too, so even when they didn't technically fit, they still worked.
Also, I'd suggest looking at a few of the capsule wardrobes that Angie has posted here to get an idea how they work. And, to be agnostic, I suggest also looking at the Vivian Files (http://theviviennefiles.blogspot.com/ ) where V. has some phenomenal examples of how to mix and match core pieces with accessories.
ALSO: Make sure that what you buy is washable. Inevitably, I would get home and have to rush around and not be able to change before the baby icked me with some variety of goo. No one needs to be dealing with the hassle of dry cleaning while caring for two babes and working. The Gap trousers were a real winner for me on that, plus I could order them over them online rather than trying to find the time to try them on in store. It's hard to find time for shopping too!
