Using "Unless" in The Past Unreal Conditional

In negative sentences, we can have two options:

We can negate both, the IF Clause and the MAIN Clause.

Example:  If I hadn't worked a lot, I wouldn't have been able to buy my house. 

Nevertheless, we can use the word "unless" followed the IF Clause in affirmative way, keeping the same meaning of the sentence.

Example: Unless I had worked a lot, I wouldn't have been able to buy my house.