although it's the law it does depend somewhat on your local immigration office as to how it's enforced, for example Chiang Mai is extremely strict on it and there are reports of Phuket and Pattaya cracking down as well.
Absolutely a run up to Mae Sai for a border bounce is the best option but a small overstay (2 days) is an alternative - I did a 6 day overstay myself at the beginning of 2016 but only because Promenada refused a 7 days extension Dec 30 as my ED (and extension of stay) expired Dec 31. \