I bought this one off of amazon and it took me a couple of house to install. It was a breeze with no issues, and my first one to install. All the wiring was already there, and I didn't have to add any support brackets. There is an additional extension you will need to purchase if your for is 8'. It's on amazon as well.

Chamberlain B503 Ultra-Quiet and Strong Belt Drive Garage Door Opener with Med Lifting Power, Blue https://www.amazon.com/dp/B0748L8NNV/ref=cm_sw_r_cp_apa_y3QtBbYG5T2BB