Josh, have you spoken with your Oly coach (I'm assuming you have a coach) with regards to devising a strength or strength maintenance program, and then adding in metcons like you'd find on Crossfit Football? You're totally correct that with your lifting background you need something more sophisticated than SS, and I think at 18 you could probably push yourself with volume beyond 5/3/1 and still see gains (provided you aren't doing three metcons a day craziness).
Another option would be investigating a Westside-style program combined with Crossfit metcons afterwards. Chris Mason wrote an article for the Crossfit Journal on combining Crossfit and Westside. A Westside template is extremely flexible and can basically require as much volume as you'd like from it, and it's pretty easy to integrate more conditioning work from it. I've been having great success from it myself and I don't have nearly the training experience that you do. An extra benefit is that Westside programs tend to emphasize a lot more posterior-chain developing exercises, which can be tremendously helpful for people with bad backs. And adding in box squats, reverse hypers, sled pulls, etc have done a LOT for my Olympic lifting, as I found that area to be severely undertrained by my Oly program (though given your PLing background that may not be an issue).