Weddingbee boards

My seamstress kept promising me she'd order a petticoat for me and still never has! I'd really like to wear one under my dress - it's a ballerina length a-line dress with a skirt of tulle and lace so I think a petticoat would make it look that much more fab! My question about petticoats are:

1. and most importantly, where should I buy one? I've seen a few on Etsy and Amazon. ANywhere else I should try?

and 2. when the measurement on a petticoat says 30" (for example), does it actually go down from waist to feet the full 30" or should I count on it riding up a little and subtract a little from that measurement? Like maybe to about 27"?

I need a petticoat that lies perfectly flat at the top, from about the waist to the hip (as if my dress had a drop waist) because the fitted bodice has a v-shape that extends to just above my hip bone. If anyone has one or knows someone trying to sell one, please send them my way!!

thanks, ladies, that's pretty helpful! I will try them both and see what else i can find:)