Steps to have your own personal relay as a double outbox/inbox relay:
Go to
https://relay.toolsClick Start a Relay
Select the standard plan
Log in with a NIP-07 extension
Pick your subdomain name for it
Hit Deploy.
After paying, the screen will redirect you to the relay settings.
Go to Access Control Mode and choose the current setting to "Block By Default and Then allow What I want".
Then on Access Control Lists / Allow Tags
Activate: Allow Events Tagged to PubKeys
Then on Allowed PubKeys, add your key
Now all you need to do is to add this new relay to your Public Outbox AND Public Inbox relays on Amethyst.