Gosh it's hard isn't it! So many factors to consider. From the information that you've mentioned I would be inclined to switch to tamoxifen if I was you. I have been on it myself for about 20 months without any problems at all. Of course tamoxifen has it's risks too - blood clots, uterine cancer, eye problems - and it is slightly less effective than aromotase inhibitors in preventing recurrance in post-menopausal women (as I now am thanks to chemo). But overall it seems to be a bit more gentle on the body than AIs.
I am not a medical professional though. Perhaps you could ask your oncologist if they can put a figure on your chances of recurrance with tamoxifen verses arimadex. If it's a matter of a couple of percentage points it might be worth making the switch. There are never any easy answers with these decisions. Good luck. I hope it works out okay for you. Janet.