Should there be a comma in this sentence?

"It is the watch that we wanted to own, but could not find."

Thanks for your help!

When two actions or thoughts are joined together by a conjunction a comma can be used; so you're sentence is fine with a comma. Personally, I take the view that if a comma makes the sentence easier to understand then it must be used. Going by that 'rule' the sentence is also fine without a comma...!

Great, thanks Tom! Sounds like a good rule of thumb!