Setting max width for body using Bootstrap

I'm building my first site with Twitter Bootstrap and experimenting with fluid layouts. I've set my container to be fluid, now the content inside takes up the full page width and adapts as I resize the browser.

The design I'm working on was created for a maximum width of ~950px.

I've checked variables.less and responsive.less, and the Bootstrap documentation; I can't quite work out how to make this happen.

I also tried adding the following to my style.css:

body {
    max-width: 950px;
}