And in the same scenario the safety could get disengaged and you're back where you started.

That's an awful lot of low probability events happening. Not that it's impossible, but it's like having a plane crash on top of you just after you were struck by lightning.

I've only heard of the Cominolli thumb safety for the Glock, but have no experience with it.

Another option might be installing the NY1 trigger spring. It'll make the trigger pull heavier, so lessens the risk of an unintentional discharge in your scenario. When I had a Glock I used the NY1/"-" connector combination, which kept the same trigger pull weight but had resistance over the full length of the trigger pull so it was closer to that of a revolver.

There's also the Striker Control Device. It replaces the cover plate on Glock slides. When pressed down, it locks the striker in place so the gun can't be fired. It's normally used as a safeguard when holstering, but in your scenario you could pick up the gun while keeping a thumb on the SCD for extra safety.

Personally, if you really want a gun with a manual safety, you'd probably be better off getting one designed that way from the factory, like the M&P.

Or you could just get a good quality holster with adequate retention and practice safe gun handling skills.

Just my opinion.