Here's a breakdown of the phrase:
* gofalwch: plural imperative form of "gofalu" which means "to take care of"
* amdanoch: prepositional pronoun meaning "of yourselves"
* chi'ch hun: means "yourself" but in the plural form
Other options:
* Gofalwch yn dda: "Take good care"
* Cymryd gofal: "Take care" (more literal translation)
The best choice depends on the context and the level of formality you want to use.