I bought 3 dresses from m+s, Really nice cross over dresses, cotton, great for work and home and still look half decent. Im 34 weeks, usually a 12, bought them in a 14 so can wear them again, and have had loads of people say what lovely clothes i have for being pregnant.
New Look also had really good maxi dresses, i bought in the summer, again just 1 size up and will wear them again.
Sainsburys also had a few cross over cotton dresses, that i have worn loads and know i would wear them again.
One thing I would say to any new Mummy not possibly knowing this, is when you get bigger up the top, be prepared to stick a safety pin in dresses, so your bra doesnt show all the time, underneath your top. Ive gone from a 36 C to a 40C and the extra amount of material up the top, makes evrything on show. Sometimes it looks like a little pretty cami top, but other times, if your dress is not a maternity style and probably made for this, it can look a bit odd.
Now with only 4 weeks, I am more and more into trackies, and i only have ever worn skirts or dresses before!