Jumpsuits are springing up everywhere. I wore them when I was a child. What I remember was having to remove the whole piece just to use the restroom. That didn't bother me so much as a kid as I know it would in perhaps a nice restaurant or something. The FP Beach Soleil Convertible Harem Pants/Jumpsuit above has the harem pant bottom that some women love or hate. The capri style is tolerable and cute with strappy flats.
The Silence & Noise Knit Strapless Jumper is for those who like the harem but want to tone it down to a more realistic and practical mini style. This is a casual and fun romper for running around town in. You can find this here: Urban Outfitters Shop Women's Apparel.
My bargain pick was the BHAGS Cotton Tube Top Jumpsuit With Pockets I found off of Ebay. It's not too loose, not too fitted, not too trendy, which for me makes it just right. Black is not featured, but I asked and they do carry it in that color. Just specify at checkout, and shipping is free!
Styler tip: These basic onesies are screaming for accessories, so go for it. Gold, silver, large and bright stones will all work.