love this dress

I really want this dress but I found it at Motherhood Maternity online and online only carries up to size XL (which is 16-18) whereas 1x is 18-20. I am a size 18 so I don't want to buy it and then have it be too small around my hips! Isn't there a Motherhood in Castleton Square Mall?

Here is the dress!!!

related side note: I can't wear my Spanx pregnant - looking for alternatives to things to wear under dresses for the summer that will a) not my thighs/calves look awful (which I guess they will be covered by a dress) b) is not super hot (hence why tights are out of the picture c) are not pantyhose - self explantory i hope um because they suck. I was thinking leggings but I haven't worn them since like 1993. And like that dress would black ones even look right? And do I get them short or long or ankle? UGH. I need help.

Edited to add: My thighs SUPER chaffe (chafe?) when wearing dresses. I've tried baby powder, deodorant, you name it to stop it and it still sucks after like a hour. So I need something under it. I have even considered super old school biking shorts. LOL oh and dorm shorts don't work because they are too short and my thigh fat is too long LOL