springy, Lily's right - lots of the women on the Tamoxifen thread have had v.similar thoughts to you. I'm so sorry to hear you've been hit. Cancer's beyond grim and it's totally up to you of course, but I thought I'd post as the more people who give you opinions the more you can mull it over.
So I had BC treatment 5 years ago. I wasn't triple negative, but it was in my lymph nodes; I had mastectomy, chemo, rads, but first like you I read a lot and thought a lot. In the end a couple of things made me accept chemo. First was trying to think how I'd feel if I didn't have it and it then came back. Would I be kicking myself? And looking at my then 5 year old, the answer was yes. Second was a neighbour who's a chemo nurse. Her advice was to 'chuck everything at it', as too many times she's seen women who've refused or who've had a good prognosis return with secondaries.
Since being diagnosed I'm met lots of women who've been through all of this. There are so many stories I could tell - lots positive, but of course lots not. One friend wasn't offered chemo as her prognosis was good so she was told she didn't need it - she had a lumpectomy and rads, but it came back in her lungs and she's Stage 4 now. Sadly I have lost count of the number of women who I've met who are no longer here, but equally there are a lot of us who've been through it all who are very much still here.
The thing is you you might know the cause of your cancer or you might not. I have always been fit, good diet, not overweight, not especially stressed and I still got it. I looked at my diet, read all the books, scoured the internet forensically, but in the end I decided all I could do was to trust my team and keep living as I had. So far (touch wood) it's worked and I'm still clear.
You call the NHS treatment 'brutal' and yes it is. It's the same across the world, and the same if you go private too. They cut bits off, poison you, burn you.. it's primal and brutal because it has to be. It's great that you've had such clear margins, and you're right there might be absolutely no need or point in chemo as your cancer has already been taken. But what if there's one cell lurking somewhere round your body? It only takes one and that's the thing that the chemo might stop.
I hope I haven't said anything annoying - I do remember (will never forget!) how overwhelming and scary it all is. Ask anything you want if it helps, but good luck with whatever you decide.