Every account in its own profile

Each profile has its own WebKit data store, so a login in one profile is not seen by another. Put work in one profile and home in another, and both stay signed in at the same time.

In a site's Site Settings, "Always open in" picks a space for that host. Links from other apps, ⌘-clicks and addresses typed into a new tab then open there. Settings › Profiles › Space Rules lists and removes them.

A burner tab (⌥⇧⌘N) has its own in-memory data store and is gone when it closes, so a one-off login leaves nothing behind in any of your profiles.

⌃1 to ⌃9 jump to a space by its position, and with trackpad gestures on you can swipe over the sidebar. Every shortcut is listed in the ⌘/ cheat sheet.

1. Press ⇧⌘S, create a new profile for each account you keep apart, and give its space a name, colour and icon.
2. Sign in to each account in its own profile's space.
3. Click the Shield badge on a site and choose "Always open in" to send that host to the right space.
4. Switch with ⌃1 to ⌃9, or turn on trackpad gestures in Settings › Tabs and swipe over the sidebar.
5. Optionally, use Edit Space… to give a work space a schedule, so the window switches to it during working hours.