I was in a similar spot 5 years ago with a diagnosis of breast cancer. I had a mastectomy and then had to decide about chemo. The oncologist was strongly for it because the cancer was stage 2, but I was on a vent and had pseudomonas in my lungs. Many people have pseudomonas and never know it. Pseudomonas is an opportunistic infection that goes dormant after antibiotics but will reactivate if the immune system is compromised. So since chemo lowers immunity, I figured I would have constant pneumonia from the pseudomonas if on chemo. Luckily my cancer was hormone receptor positive so I went with Tamoxifen tablets and radiation rather than full chemo. Now past 5 years with no recurrence.
None of this applies well to your situation, but remember that chemo may not be required and if it is, it is not as awful as it once was. And radiation is a real nuisance, being daily, but it is a possible option. Hang in there!