First off, do not get orthotics! Avoid them at all cost! Secondly, Nike Free's are not really considered minimal at all and they have a very high heel so they could potentially add to more knee problems. I would recomend some light barefoot running on grass. Minimalism isn't usually a quick fix, it takes time for your body to re-learn how to run. Barefoot running will help with that. If I were you I would switch into a shoe like the Adizero Pro, and stay at low mileage until your body gets used to the new way of running. You need to train yourself to land more on your forefoot, this is very easy to do while barefoot but it can be hard in trainers that have high heels. Good luck.