Every bootstrap theme is easy to modify, either through LESS or CSS. You can even have a theme selector if you want. The grid for a basic theme is easiest to start with like this http://wrapbootstrap.com/preview/WB01KF12C which is a very nice theme.
For more resources check: http://mashable.com/2013/10/20/bootstrap-editors/ and http://bootstraphero.com/the-big-bad...trap-resources

//Morgan