@tothelefttotheleft
Sorry to hear you were diagnosed with cancer, but welcome to the thread.
It's great (in the context cancer of course) that you're stage 1. Grade 3 is annoying. Mine is also grade 3 (and stage 3 though).
You asked about whether you can avoid chemo and radio if you opt for mastectomy. Obviously that's something for your MDT to answer, but certain things will depend on your subtype of breast cancer such as:
ER+
If you are hormone positive, specifically oestrogen (ER+), you have much more of a chance that you will get away with less harsh treatment. ER+ cancers are slower growing and have a better prognosis, but grade 3 is the fastest growing of the 3 grades (grade 1 is very slow in ER+).
HER2+ or TNBC
If you are not oestrogen positive, you will probably need chemo and radio anyway, even stage 1 grade 1. Then you'll be Her2+ or triple negative, which are the aggressive ones, and tend to also be higher grade, so 2 or very often 3.
You'll need to find out your subtype as above to know more; that will tell you a lot about your specific situation.
I know a few people with ER+ who did need a bit of chemo (far less than I did with Her2+ Er-neg). They were grade 3, stage 2.
Do you have a CNS or oncologist yet? I hope they'll let you know your treatment plan soon. Waiting is horrendous.