Wash what is practical to wash - so duvets, dog bedding etc.
The things that are not practical to wash, that you do not come into direct contact with (although it is safe once dry) - under the seat cushions on the sofa, under a mattress topper.
I have never washed sofa seat cushions or indeed sofa covers -its the cracks/crevices that are where the flea eggs go.
Fleas live on the dog - however most of their life cycle takes place off the dog!
So fleas heave their eggs overboard. These are then jiggled and bounced into your carpet and down the side of the sofa cushions or under the mattress.
They hatch into itty bitty larvae, and they feed on detritus, skin cells, hair, flea dirt... importantly, they will eat tapeworm eggs. Remember that part.
They pupate, and then hatch into fleas, and then hop onto your dog.
Your dog itches/licks himself, ingests the flea and the tapeworm eggs survive the digestion process and now your dog has tapeworms too.
So the flea that hatched and had its larval stage at Auntie Joans house, where her cats have both fleas and tapeworms, or in the nest of some feral cat that your dog walks past every day... hops on your dog and comes home with you... and ick. Itch. Yuck.
So ensure you are de-fleaing and worming appropriately, with vet approved stuff not over the counter (it is at the same time, not overly effective at killing fleas, and still a high risk of causing harm to the dog!).