Yes, ATMs are widespread in both Chiang Mai and Bangkok. In Thailand, most ATMs are on the Cirrus and Plus networks, which covers nearly all internationally recognized debit and ATM cards. For foreign cards, Thai banks currently levy a THB 150 fee on top of any fees incurred by your home bank.
As we are not medical professionals, we are unable to offer professional medical advice. We do recommend following the recommendations of your family doctor along with reading and following the recommendations of the Center for Disease Control's page for travelers to Thailand.