"I would like to have a cleaner house than I had last year."
Translation:Jeg vil gerne have et renere hus end jeg havde sidste år.
Why not "Jeg kunne godt tænke mig at have et renere hus end jeg havde sidste år?"
I think that could also work. "Jeg vil gerne have..." is a pretty common set phrase, akin to "I would like..." in English.
You are correct, both could work and both are quite idiomatic.