No more long-lived access tokens, whats the best strategy for own account usage?

While the creation of new long-lived access tokens is now deprecated, we don't currently have a plan to disable existing long-lived access tokens. (If that changes, we will of course announce that ahead of time.) That being the case, you can continue using existing long-lived access token(s) without interruption. You are not required to migrate existing long-lived access tokens to short-lived access tokens. Note though that after the change you won't be able to create new long-lived access tokens.

In your case, if you did want or need to migrate (e.g., if you accidentally revoked your long-lived access token after the change), you would need to process the app authorization flow for your own account once, and store the resulting refresh token, so the app can programmatically use it to get short-lived access tokens for your own account as needed.