further to sarah davachi mentioned above, in terms of classically-influenced drone/‘dark ambient’, you could do a lot worse than ellen arkbro’s for organ and brass, aine o’dwyer in general, maja ratkje’s the crepuscular hour, and this pancrace record
nicolas szczepanik is a top lad - a fair few one-track records of magnificent, emotional drone
I also really rate the band/bloke ore, who make doom with tubas - not ‘abrasive’ per se, but more metal-tinged than you might be looking for. plus the guy is a good egg and used to put on experimental music nights at a parish hall in the middle of nowhere in worcestershire which i appreciated heartily.