I personally didn't want to take 6mp or Imuran either but the idea of an accident scares me a lot more than the repercussions of these medications. They have been around for a long time and have good safety statistics.
I think you may see more benefit from Rowasa if you're inflamed. Perhaps Rowasa in the PM and Canasa in the AM for a while and see how you do? Even a steroid enema before bed may be helpful and it's better than immune supression if it's not warranted. You can always taper off the steroid enemas after a few weeks and hopefully maintain on 5ASA rectals.