If hormones are completely contraindicated for you, can you take a low-dose of something like Ambien? I know it’s probably not what you would prefer to do, but having severe insomnia and not getting sleep is just not healthy for the body.
Of course you know that, and I am so sorry that you are struggling with it.

I believe there is some controversy around the issue of breast cancer survivors and HRT. In some instances, I think depending on the patient, their particular medical history, and their specific type of breast cancer, they can use some forms of HRT. But I don’t know enough about it - have only read it in my own research on HRT. You may want to look around and do some research on that.
I have found for myself that using a meditation app on my phone at night has helped a lot! I didn’t think that it would, but it did. Also, things like Valerian root, and maybe even melatonin? I wish I could offer you more options. At some point I think it’s important just to get the sleep, even if you have to take something that you would prefer not to. Let us know how you’re doing!