My understanding of legal separation is that it's just one step closer to divorce. That's why I would not opt to do it. But you are in your shoes and this is a choice for you and S.
My W and I had an attorney draw up a legal document outlining a few things, most importantly finances. It's not legal separation but it offered her some level of protection and comfort.
AKA: "Ben the school teacher" --- Me:45, W:41 | Ds:10,12&14 | M:18, T:20 Me: MLC+PA+WAS+Separated 10/08 My Request to Reconcile Denied 7/09 W w/OM 6/09-11/09