In the UK there's a product to go on the rafters when the
roof is covered with straw. It's a firestop for 1 hour
at 2000F. That's all I can help you with but it's
well known and I'd say to look at the BBC show called
Grand Designs .. one where a straw roof caught fire and
the roof was replaced.. in about 2006. You might be
able to follow up on the product name there or by
looking for sites limiting to the UK for fire stop.

use google this way to limit to uk.

site:.co.uk fire stop roof

the site:.co.uk
limits to UK sites

the latter words are what you're looking for. I've tried
it and it works.

Good luck.
Andre

"painting everything black to give it the illusion of highe ceilings"

This is a really bad idea. Black ceilings are not going to make a basement look taller. It will just look like a cave.

I watch the show INCOME PROPERTY on HGTV.
The guy there always puts in ROCK WOOL as overhead insulation between floors. He also has other materials to serve as a fire break, but I am not able to speak with any kind of authority.