I am incredibly fond of dresses. While my favorite, most flattering style of dress is probably the fit and flare, if I was forced to choose one single dress to wear it'd have to be the basic shift. It's the dress I would recommend to everyone as a must-have. It's endlessly versatile and easily remixed. I have wide hips, which I think discourages most people (myself included) to buy shift or sheath dresses... because honestly, who wants a dress that's super tight around the hips, and loose everywhere else?
My advice would be to buy a size up, for a comfortable fit, and fall in love with the many ways to style this wonderfully basic dress. Belt it for the fit and flare that you love, or tuck it into a skirt. Wear it plain with a loose cardigan for a super cozy feel, or throw a sweater over it because it's so easy.
I've been self-conscious in the past because of how much I wear this dress. But it never gets old (to me - I haven't polled my family and friends). God bless the shift dress.