More literal translations:
* Cartref melys cartref: This translates directly to "home sweet home," but it's not a common phrase in Welsh.
* Cartref ciwt cartref: This is a more playful translation, using "ciwt" (cute) for "sweet."
More idiomatic expressions:
* Cartref yw'r lle gorau: This means "Home is the best place."
* Dim lle fel cartref: This translates to "There's no place like home."
* Yn ôl adref: This literally means "Back home," but can convey a sense of longing for home.
Ultimately, the best way to express "home sweet home" in Welsh depends on the context and the tone you want to convey.