Lastpass is a great choice. It is smart to have password managers such as Lastpass generate the strong passwords for you and save/manage them. So you could use Lastpass to save your posting/memo password as well as store a separate active password.

Normally, you would be logged in with the posting password (see this guide for details). But you can temporarily log in (in a private or Incognito window for example) using your active password any time you want to do any operations other than posting or voting. That includes powering up or down, sending money to other accounts, using the internal exchange, or changing your active, posting, or memo keys. Then once you are done with that privileged operation, you can logout or simply close that Incognito window, and go back to using your normal posting login.