At least with my in-laws, Christmas in Mexico is waaay different than what I am used to in USA. in the US Xmas Eve is for midnight mass and wrapping/stuffing presents under the tree and then the family all gathers round in the morning to open presents. In Mexico, Xmas eve is a huge family dinner party where folks begin to arrive at 10pm, a break for a family service at midnight, then dinner followed by family game night, desserts, family stories, etc until after the sun comes up (I usually give out by 4am). There is no gift opening Xmas Day because that is not done until el Dia del Tres Reyes (Three Kings Day) on Jan 6. So the rest of the morning is spent sleeping it all off.

No recommendations on where to eat, only an observation supporting what you already found - there should be plenty of restaurants open.