The Lane Bryant catalog is actually not related to the store at all; they basically license their name to the folks who put out the Roaman's catalogue. Having had a very bad experience the one time I tried to order through them, I won't again.
Motherwear I think has a maternity catalog with some plus-sized clothes at about the same price point as Lane Bryant. Gap & Old Navy both go up to about 3X in their online maternity. Of course, if you're able to spend Lane Bryant prices and willing to buy from a catalog or online, enter "plus sized maternity clothes" into a search engine. There are a TON of online boutiques that carry plus-sizes.
As to the wearing larger clothes...That's what I did last time and what I am doing now. I was a size 18 last time, so I was actually able to pick up a few pairs of pants at Target for $20 a pop and I wore them constantly. I have never been able to wear maternity tops. They are just cut poorly; apparently large-breasted women never get pregnant. So for tops I have always worn street clothes, and I got through the first trimester twice in the past with about three drawstring skirts (I cannot stand to have
anything binding my stomach the first few months, so drawstring skirts let me go underneath my tummy). Right now I'm surviving on the few size 22 bottoms I kept to sell online.