I agree with Willow. I work in IT, and with some things I could get by with just getting a size larger than normal.
One thing to keep in mind is that from your ticker its your first time TTC? Everyone puts on different amounts of weight when pg, I put on 30+kg and need the maternity clothes, but a lot of my friends only put on between 6-10 kg, some even less, and found they didin't need all the expensive maternity clothes, so maybe don't go out and get everything all at once, until you know whether you will in fact need it - you might saty in your regular clothes!