For a good stay location search for properties within the walled old city, not near central city area. Recommend to book an Airbnb for couple of nights then search for monthly accomodation locally. Nimman area has lot of co-working spaces and all the Digital Nomad cafes. You can get accomodation within THB 4000-8000 with WiFi, electricity and water costs.
Akha Ama Coffee shop is a useful place to get work done. It has free Wi-Fi and plugs.
Punspace has really fast internet and costs about $9 per day. Great people around here. They have another outlet at Nimman too.
Chiang Mai International Airport (CNX)- you can get a free sim card in the luggage area or few stalls, Card is free, so you only pay for the usage.
DTAC or AIS (Happy) sim cards and recharges are available at all 7/11 shops throughout the city.
Great place to work with fast WiFi, comfortable seating with an outdoor section too. They have power outlets and really nice espresso. The staff is friendly. Definitely one of the popular spots with Digital Nomads.
Camp by AIS is located on the 5th floor of Maya mall. It's a cafe cum coworking space, with both locals and other Digital Nomads. They have super fast wifi though it can get noisy at times. Try the lemon tea there.
Chiang Mai - Soi Nimmana Haeminda. This area is full of cool cafe, restaurant and shop. Digital nomads everywhere. I have been stay there for a month. Very cheap and safe. AIS Internet speed was fast specially at CAMP co-working space. It is located at Maya life style shopping center. If I come back to Thailand, I will definitely stay this area. Not downtown, but cool enough.
Camp, fifth floor of the Maya Mall, Nimmanhaemin area. Free co-working space style cafe where you can buy a coffee or food to get free WiFi for 2 hours at a time. Excellent internet speeds and despite the vast size of it, pretty quiet it terms of noise. Power points everywhere and meeting rooms for hire.
Using your passport you can get a SIM card from AIS or Truemove (outlets in Maya Mall and Kad Suan Kaew Mall respectively). Get 2g for a month for 350 baht or bigger packages and tether to your phone to work with no problems at all. Can also connect to the provider’s WiFi hotspots throughout the city for free if you have a package.
You can extend your 30 day tourist visa to 60 days at the promenada mall (bottom floor) for 1900 baht. you will need your departure card / visa stamp / passport photocopied and signed, as well as a passport photo. both of which can be done next door to the office for 204 baht. closes at 4:30pm, took me two hours. don't overstay or you will need to leave the country to renew your visa and pay 500 baht for each day.