> for the purpose of permanently and privately storing my data, ...
What you want is only possible with the relay that you control. If you are a technical person you can spin up your own relay.
Discussion
I'm not. My brother is a reasonably experienced software developer. Do you think he would be able to do it?
Probably yes.
Here's a quick overview of relays.
Your brother will be able to find a way.
https://voltage.cloud/blog/nostr/the-essential-guide-to-nostr-relays/