So are you thinking an interlock switch such as this?
Generator InterLock Kit Manual Transfer Switch
You'll need another 240V "inlet" (not an outlet, as you don't want to use a home-made male "suicide cord" with a hot plug end if your gennie is running). But, YouTube installing a 240V outlet/circuit, and this should pretty much give you the info you need.
The other option w/o disconnecting at the meter is a transfer switch where you need to tie into individual circuits. More work, of course.