Solution:
After a long search I found a really good tutorial on how to recompile twitter-bootstrap to use in WordPress admin. You can find it here.
Using Bootstrap 3
Create a new .less on the same directory where your bootstrap.css is (for example wordpress-bootstrap.less) and wrap the following
.bootstrap-wrapper {
@import (less) url( 'bootstrap.css' );
}
… after all you have to recompile your css (I used winless) and you get wordpress-bootstrap.css wrapped inside .bootstrap-wrapper.
Then, you’re ready to go!