Bedroom bed question?

Heyy my other question is on how to make a small room better :) well I came to thinking canyou get a bed that is a single but at night I can easily turn it into a double bed? And if so can you do this everyday and night ? Are they comfortable ? And I mean like the single bed converts to a solid twin/double bed? I'm asking all this as I know some beds are for Occasional use hanks everyone :)