[all variants] Lubuntu ruing slow on netbook

Hey all. I've been using Lubuntu on my home computer and netbook for quite some time now, but over the last few weeks there has been a significant decrease in performance on the netbook. I'm going to upgrade to 16.04 and see if there's a change, but maybe its just that Firefox is too bloated now. I was just wondering, is there a way to install a pre-configured ubuntu distro but with a fluxbox or lighter weight window manager? I was thinking of trying Debian with a light window manager, but I think configuring the whole system securely is a little beyond me, hence why I'd like to stay in the Ubuntu family for now. Thanks in advance.