Jeans from Topshop are good-nice strong shape that withstand wearings and washings. whichever you choose, you will find yourself undoing buttons, taking them off at the end of the day.However- I really didn't want to go down the 'I just want to be comfy' look and end up in tacksuit bottoms at 25 weeks til the end- too depressing.
Tights- Urban outfitters bigger size are great. I didn't bother with maternity but neither did I go cheap. Your normal knickers will see you through no problem. I have stored my reallynice lingerie away and am wearing my 'tier two' knickers. Going to wear them til the end, not care if I mess them up post-partum, then got out my good stuff when I am ready and buy some brand new bra and knickers. See it as a chance to wear out some not so great knickers.
The biggest disappointment have been some quite expensive Seraphine tops and jeans-jeans are massive on the thighs and tops WAY to short. Just wear your longer tops/summer and spring dresses over your jeans and if you need to supplement, go for some cheap, tubey stretchy dresses for over your jeans or leggings. Yu can still wear your cardis- don't go mad on maternity 'knitwear'. Looks frumpy and so so aging and you are better spending £60/£80on a really nice lightweight maternity mac to see you thorough spring summer and a n other pregnancy.
Try and hunt down some REALLY long, close fitting vests in black and white- I mean sort of top of mid thigh, to go under other tops.
Couple of nice scarves to trail over bump to make you feel less naked if out without a jacket in early summer.
A few spare plain cotton pyjama bottoms for the evening when you get in from work. You can keep your plain tops on, put your bottoms/slippers/wooly socks on and still look quite nice rather than worn out scruff. Exception to the knitwear rule- a nice long wooly cardi is useful for evenings at home. Much better than depressing dressing gown, and less 'invalid'.
Gap always got some good plain maternity basics in a constant sale- siad tube dresses,long cardis for eve, plain tops.
Avoid shirts for work-look messy. don't go mental with jewellery esp earrings. Those two things apply anyway