To play Blues Harmonica you will need a 10-hole diatonic harmonica in the key of C. This is what I use for the vast majority of lessons in the Online Harmonica School.

I recommend the Hohner Special 20 for beginners. You can buy one directly here https://amzn.to/2WX9q0M (This is an affiliate link - I do get commission so please don't feel obliged to use this link)