Maternity sizing?

Kelsey • Happily married•Mommy to a sweet princess and 2 boys• One on the way•
I'm kind of scared to order anything offline, as I did recently in a L, which is what I would normally wear and it was HUGE. I don't have anywhere close to home that sells maternity clothes, and I'm really just looking for tops. Any ideas on online places that run true to size?