I use to have to add Mystik SAE 30 everytime I cut grass. I used Amsoil XL 5w30 and consumption went away for several months, then it required a couple of ounces. I then put in Amsoil 0w-40 and consumption ceased, while still keeping good (better than Mystik) fuel efficiency.
First, I would suggest trying to clean the motor out with some kerosene. Next time you need to add oil, just add kerosene to top it off, then let it idle for 15-20 minutes, drain the oil, and use a cheap synthetic (Super Tech) Xw-30.
If that doesn't bring the consumption down, then bump up the weight.