Hi Kim22
Your boss is a bit of a problem, isn't she? While I am all for positive attitudes, that doesn't really cut the reality. But practical things to think about - I too had HER positive cancer, mastectomy, chemo, herceptin and hormone therapy. I worked through treatment. I liked my job, my boss was very supportive and I didn't have nausea or fatigue. Hard to tell what your reactions will be till you start, there doesn't seem to be much rhyme or reason. Like you, I told my staff at the outset - they were really helpful. I also had them on chemo brain watch, just in case I started losing it! But I didn't. I got tired but only when I had work reasons to be tired (i.e. the normal ones!) and I certainly got tired of having treatment but I think that's pretty normal.
After the the active part of my treatment wax finished, 12 months on, I changed my job and chose to go to a 4 day week. It was much more about making time for other things and my age than about cancer, although I have no doubt that the thinking you go through when faced with something like cancer had its place too.
I am 4 and a bit years on from diagnosis, feel good and getting on with life. As others have said, this is doable. Lots of people can advise on specifics as you need them and while the work front is a little tricky, the one day at a time advice is very true. Half the things I worried about at the outset never happened, other things cropped up from nowhere. You can waste a lot of energy overthinking things too far ahead.
Very best wishes.