Your Boycott-itarianism could work just through market signals. As long as your diet makes you purchase less high-cruelty food and more low-cruelty food, you’ll increase the average welfare of farm animals, right? Choosing a simple threshold and telling everyone about it is additionally useful for coordination and maybe sending farmers non-market signals, if you believe those work.
If you really want the diet to be robustly good with respect to the question of whether farm animals’ lives are net-positive, you’d want to tune the threshold so as not to change the number of animals consumed (per person per year, compared to a default diet, over the whole community). One would have to estimate price elasticities and dig into the details of “cage-free”, etc.