When I was pregnant the only decent maternity lingerie I found was HOTmilk...
http://www.hotmilklingerie.com/ although their current range isn't as nice as it was back in 2009 
http://www.cakelingerie.com/
You're right there definitely a real lack of nice maternity lingerie.. not all of us want to wear bridget jones pants and tent bras for 9 months 
There is nothing "wrong" with normal underwear they just advise pregnant women avoid wearing bras with underwire. The above advice of babydolls is great!