I've never heard either of these. You'd say "lie down on the sofa every day" or "nap on the sofa every day."

These are colloquial English, specific to the UK. The sentences are fine but there is a subtle difference in meaning. If you doss down somewhere you normally sleep without a bed, on a floor, couch, or the backseat of a car etc. But when you bed down it implies only that you are sleeping somewhere other than your normal place of sleep. for example. I'm gonna doss down in the back of the van tonight. I'm gonna bed down at my mates house. You can also use doss on it's own, this would mean that you were sleeping rough. I've been dossing in an abandoned building behind the old iron works since my parents kicked me out.

Thank you, James.

Thanks, Duncan.

I'm from the UK and I've never heard doss down before. You can say bed down, but I wouldn't say it was particularly common. "It's time to bed down for the night". When I hear this though it sounds like camping, perhaps even hiding out, covert camping. In slang terms you might say "My uncle likes to crash out on the sofa all day".