The adjective contentus (satisfied, content) can be modified with ablative.
For example, viro contentus means "satisfied with a/the man".
In your case the attribute has two words: unus vir (uno viro in ablative).
Therefore I would translate like this:
Uxor, quae bona est, uno viro est contenta.
A wife, who is good, is satisfied with one man.
I added commas to make the relative clause clearer in both languages.
If you drop the relative clause altogether, you can see more clearly how contenta works together with uxor and the ablative attribute.
Let me also comment on your attempted translation.
- If you want to say "a man is satisfied", you should write vir est contentus.
Notice that vir is the subject and therefore in nominative, and contentus follows the gender of vir.
Therefore translating viro est content as "man is satisfied" fails for two reasons.
- The relative pronoun is quae and the relative clause is quae bona est.
A relative clause can well be inside the main clause.
The main clause is Uxor uno viro est contenta.
- The numeral uno can be thought of as an adjective attribute of of viro.
It just emphasizes that a wife should be satisfied with one man.
One could read the sentence as Uxor, quae bona est uno viro, est contenta ("A wife, who is good to one man, is content").
This feels unlikely to me, but it is grammatically a valid interpretation.