a safer no password sudo?

Try adding this to your sudo options:

Defaults timestamp_timeout=0, tty_tickets

tty_tickets option (on by default) will make sudo ask password if it was not asked previously in that particular tty (including terminal emulators ptys), and timestamp_timeout=0 option will make it not ask it again in the whole session.

So, when you want to do some administrative operations, you can open terminal, sudo something, close it, and you will be safe again.

The obvious solution to me is to reduce the complexity of your password. You seem happy to go for no password rather than a long, complex one, so why not look at this middle ground as a valid option?

If your machine is connected to a network then there is a risk of compromise. With no password, you do open yourself up to opportunistic exploitation, so even a simple password offers extra security.