Hi
Can't answer re Chiang Mai. but 'serviced apartment' - we had one before finding long term accomm when we moved to Phuket.
'Serviced' for us meant bed made every day, fresh towels daily, sheets weekly, supplied with small soap/shampoo/toilet paper, 2 bottles purified water (can't drink tap water there) and a quick general clean. I imagine the level of service will vary depending on fees - they also offered laundry service but at a much greater price than taking to to a laundry ourselves and collecting the next day.
We holidayed in CM last December - and will be back late this year, nice place. I think you'll find there is a specific CM web forum if you search.
Best wishes for your retirement