Just wanted to pass on a tip. I got some pjs from M&S last week - not maternity, but in usual nightwear range they have several different colours/designs in separate bottoms/tops where the bottoms are the yoga type trousers with the soft stretch waists that you fold over. I was able to buy bottoms in 1 size bigger than usual, and tops in 2 sizes bigger that comfortably fit over my bump with some room left to grow (I'm 25 weeks with twins, so quite big already). Much cheaper than maternity pjs I've seen and should also be suitable for afterwards. If you prefer strappy tops and/or some additional support, vest with secret support shelf come in colours to match.
I also got some nightshirts from there with fronts that unbutton, so suitable for bf, to wear in the hospital (mum advised get nighties in case of catheter) for only £12 each.