I need better protection of my private key... The fact I have to enter it into these sites scares me :(
nostr isn't an identity backup. nostr *is* the identity. here's how to create a backup of it!
run your own relay. that's it!
you can do this in a multitude of methods. here's just a few simple examples to get you started.
on Android you can run a relay on your phone: https://github.com/greenart7c3/Citrine
on Windows you can run a relay on your computer: https://github.com/CodyTseng/nostr-relay-tray
on Umbrel/Start9/Mynode you can run a relay on your own server: https://apps.umbrel.com/app/nostr-relay
https://github.com/Start9Labs/nostr-rs-relay-startos
if you want a DIY method, you can run a variety of relays too:
https://github.com/cameri/nostream (i use this one.)
https://github.com/hoytech/strfry
good luck!