Multisite options

I am sure variations of this have been asked many times but I hope someone can point me in the right direction.
I have one site since the 2.x days installed in /bl/ and I want to turn into multisite, what are my options?
Many threads here and elsewhere and on http://codex.ww.wp.xz.cn/Create_A_Network say that ‘Giving WordPress Its Own Directory’ will not work but the ‘Giving WordPress Its Own Directory’ is about installing WP in a subdirectory but having the site in root, right? This is not the case for me.
In my case what are my options and what will the urls look like after multisite? Thanx