1980's sci fi book series, subspace is a sponge, young man in emergency suit can propel himself by sucking in the sponge stuff

Question

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.

Answer 1

I think this might be the Kerrion Space trilogy by Janet E. Morris.

I can't be certain about this because I only have the third book in the series Earth Dreams. But in that book there is a drive that works exactly as you describe. Indeed it's actually called the spongespace drive.

The Kerrion family are the absurdly rich dynasty that control access to the spongespace drive. The main protagonist is Shebat, who is a poor girl adopted into the family when she saves the life of a family scion Marada.

The Wikipedia article for the first book Dream Dancer includes:

The Kerrion Empire’s semi-sentient Cruisers fly through “sponge” space and give the Kerrions vast control over the majority of the civilizations encompassed by the Kerrion Empire. Against considerable odds, Shebat qualifies as a cruiser pilot, which involves interacting with the cruiser’s intelligence. In the midst of a family political crisis, certain members of the Kerrion Family see Chaeron’s new bride as a threat to their power and arrange for her to be sent back to Earth and stranded there.

I would guess that the young man lost in spongespace is a plot in one of the first two books that I don't have because I found the following reference to it in Earth Dreams:

No one liked to think about the vacuum-breathers, the sirens. They existed nowhere but space-end. But Chaeron thought about them, examining each siren face he saw in Danae's monitors—one of the sirens, farting bubbles as they dived in space-end's warm plasma, might be his brother, Julian, lost to sirenhood in the Shechem war.

Presumably Julian is the lost young man, and it does refer to the flatulent propulsion.