While nothing is completely safe, I believe that covered FS is actually safer than a covered BJ because teeth can do more damage to a condom than a pussy can.

So you can move up to covered FS knowing that you aren't putting yourself any more at risk than you already are.  (Except that once you start FS you'll start to hobby much more, and that increased volume will mean increased risk.)

I am not a medical expert or anything.  The above is just my opinion.  It may be wrong.