chang rai has a very friendly immigration office. The staff will personally guide you and help with getting insurance and all the other bits needed for the visa. Don't trust agents and lawyers. Hope that helps
It's pretty straightforward. You need to deposit 800k thai baht and leave it there for min 3 months. If you goto the immigration they will freely guide you. My brother found the office in chaing rai particularly friendly. They immigrantion office helped him get hia insurance and guided him on each step. Do not use lawyers. That is my advice. I lived in Thailand for 20 years but now here until kids schooling is complete