Adding safety switch between meter and panel
There's no point to adding a switch here
Since you will have to move the meter-main anyway, which'll require PG&amp;E to cut your service drop and reattach it at the pole, there's no point in adding the extra switch you describe.
So, why can't the new meter-main go where the old one did?
Well, the NEC simply requires clear working space (110.26(A)) around the meter-main, so why can't it go in the garage? The answer lies in the fact it's a meter-main, and thus invokes your utility's distribution rules about meter location.  In your case, they're found in PG&amp;E's Greenbook, which states:

5.3.2. Prohibited Meter and Service Equipment Locations
The following locations are not acceptable for electric meters and service
termination equipment.

...

F. Inside garages for single-family residences.

So, since you'll need to move the meter there, and probably use a meter-main for that job, I would simply fit a Class 200 EUSERC meter-main, suitable for overhead service, at a suitable outdoor location. Then, you can have your 200A indoor panel set up in the garage as a subpanel from the meter main.