I read a couple of sci fi books in the 1980's from UK library, they were from a series... I don't think I read them in the right order so I've a mish-mash of memories. From the context of romance and having a female protagonist I'm assuming it was a woman author.
A family controls a sub space drive and thus is incredibly wealthy as all starships are licenced/leased through them.
The drive makes space appear sponge-like, a thick ether, one part of the galaxy is very thick with this.
A young man falls from a cargo hatch into this section of space, thanks to him being fitted with some kind of very thin emergency suit he survives and transforms to a near mindless creature. He can propel himself around by sucking in this sponge stuff and farting bubbles! (I'm fairly certain that phrase was used in the book)
His mother or big sister is high up in the Family and therefore a search is made through the foggy stuff. There are others similar to him floating around in it.
Most of the main story is high level politics and business with some kind of romance happening between two opposing families, a bit boring.
Basically my main memory is the sponge stuff and the unfortunate young man.