using translucency will depend on the type of textile and mostly the shape will be a criteria to use translucency. For couches I don't think its useful because you dont need the light to pass trough the couch, you should play with fallofs or fresnel index if you dont mind not going phisicaly accurate.
I usually do a falloff material with the same texture on both channels, but one of them a little bit darker, then play with the IOR of the mix (there are tables of reflectance and fresnel values of fabric materials online), most of the time that will do. But you can keep adding a mix material or a composite with softlight blending and use a procedural map for randomness (smoke can work well)
image source "Everything has FresnelDecember 5, 2010"
http://filmicgames.com/archives/557for aesthetics reasons sometimes making your own falloff curve will work because when adding a bump (and tiny like 1 or 2mm) to a textile the real fresnel value will not show those little "bumps" so you should make the curve a little bit steep at the end.
most fabrics are lambertian right?? (real question xd) and they have a really low specular value, so maybe in corona it's better to "fake" them only with diffuse+fallofs and zero reflection or other stuff.
and about the images, I really like the lightning ...only small stuff I notice (as well as others) couch and chair not touching the floor, no railing in curtains (would be nice to see some metal there) and the chromatic aberration in the backgroud photo, there's a purple fringe there that's look really annoying xd ..
cheers!
