I’m planning on staying in Bangkok for 4 months. I will not be working I’m retired and have a large amount of passive income coming in. What type of visa do I need to require.

You may want to consider obtaining a six month tourist visa. In that way you are not required to report your income to the Thai Authorities as you would in applying for a non-immigrant O-A (retirement) visa. Instructions for applying for all visa categories can be found on the Royal Thai Consulate or Royal Thai Embassy web sites.

If you over 50 yrs. Old u can apply for non immigrant visa "O-A" or for now single entry tourist visa will do

Go to the office they will give you more info.