I have my fire extinguisher under the driver side seat, under my legs. I use the Bracketeer; easy to find and easy to grab. I sit with the seat completely upright and pretty far forward for my height (5'10") and can still move the seat forward about 2-3" if I wanted to, so there's still plenty of adjustment, even with a 2.5lb extinguisher.
I don't feel as though I'm compromising anything having the extinguisher under the seat. Having it under the driver seat means my passenger doesn't have to deal with it being in his/her footwell.
This might be for you! It’s a handy way to mount an extinguisher in front of the seat without drilling any holes. It’s a little spends, but universal. It worked perfectly in my Forester.Bracketeer
I have a standard ABC fire extinguisher. They key is to make sure it's easily accessible. Something such as this....
https://www.amazon.com/Bracketeer-Extinguisher-Bracket-Universal-Vehicles/dp/B015G3QXMY
puts it where you can grab it as you leave the car.
https://www.amazon.com/dp/B015G3QXMY/ref=cm_sw_r_apan_glt_fabc_NWKWHCBHT7EAJHQ8Z4P4 it's called the brackateer
It's more complicated than that though otherwise the list of IIHS top safety picks would have at least one EV on it... To be fair though the Bolt didn't make the list for it's headlights, not a category I think I'd include on a list of what I think most people consider "defensive" safety.
And you're totally right, for either gas or EV cars to light up takes a serious collision with the exception of almost freak events for either type of car. The increased danger with EVs is the lack of needing an ignition source, and the difficulty in extinguishing a fire. Any standard ABC fire extinguisher will be effective on a gas fire provided it hasn't gotten too big or you're trying to use one of those teeny extinguishers. An EV battery fire is considerably more complicated...
And just to reiterate, I'm in no way saying EV fire dangers are something to actually worry about; I was just disagreeing with the premise that they're safer. In the real world we should all be more concerned with a run of the mill non-fiery car accident, choking, or slipping and falling in the shower. That is to say all I'd recommend is to mount an extinguisher in your car (no matter what kind of car) and move on with your day.