present perfect vs simple past - I've just bought vs. I just bought vs. I bought

I bought an English grammar book 3 weeks ago. Is it correct to use any of the following sentences interchangeably to tell my friend that I bought the book, or is there a difference in meaning between each sentence?

1. I've just bought a book on English grammar, and it looks pretty good.


2. I just bought a book on English grammar, and it looks pretty good.


3. I bought a book on English grammar, and it looks pretty good.