Hook: Floor Medium Narrow (Blue Rectangle)The Selkath Couch decoration fits into a narrow blue medium rectangle floor hook.
Hook: Floor Medium (Blue Square)The Selkath Couch decoration fits into a blue medium square floor hook.
How to Get a Selkath Couch Decoration
Cartel Pack Decorations
The Selkath Couch decoration can be dropped from Gatekeeper’s Stronghold Packs, which were released on the Cartel Market and bought with Cartel Coins. Cartel Packs, including the Gatekeeper’s Stronghold Pack, include a random selection of items from the Gatekeeper’s Stronghold collection of items. You aren't guaranteed to get a Selkath Couch decoration from a Gatekeeper’s Stronghold Pack, but it is one of the few ways to get a Selkath Couch deco apart from buying it on the GTN from another player.
If you're looking to get a Selkath Couch, the easiest way to get it is to head to the Galactic Trade Network (GTN) in SWTOR and buy it with credits from another player. If it's very rare and not available on the Cartel Market, you could try buying from the GTN and hope you get it.