Most countries will not deny entry to a citizen even if the citizen's passport is expired.

You don't say when next year you are going and you don't say where you are located, but since you have at least 4 weeks why not make an appointment at the nearest Mexican embassy/consulate and get your Mexican passport renewed? It might take a couple of weeks for the appointment but assuming no irregularities the new passport should be issued in about 2 hours the day of the appointment.

My family always gets their Mexican passports processed here in the US because it is so much faster and convenient than trying to do so in Mexico. If you are thinking to get the passport renewed while in Mexico you will do well to check this out well before going - they generally do not allow "walk-ins", appointments can take many weeks to schedule, and the appointments typically take many hours - not to mention the documentation requirements are much more stringent than at embassies/consulates.