The Amphur Bangrak is the most foreigner friendly district office in Thailand. Many foreigners register their marriage in Bangrak. You will need to have your letter of affirmation as well as your passport to register your wedding in Thailand. If you are going to register a prenuptial agreement then you will need to speak to a lawyer in Thailand about this as it has to be registered with the marriage at the same time. Always take proper legal advice when getting married as you might want to change the surname of your wife at the same office after marriage.
If you live in Prakhanong then you will need to contact the Amphur Prakhanong to register your marriage in Thailand. You will require an affirmation agreement or freedom to marry letter which you will need to get from your Embassy in Thailand. If you are going to register a prenuptial agreement then you would have to speak to a lawyer in Thailand for more information as they have to be done at the same time.
The Amphur in Pathumwan is here you have the ability to register your marriage as well as register a divorce. The address for the Amphur Pathumwan has been added below and you can find this online as well. If you are going to get married then your will have to contact the Amphur or District Office in the area. Speak to a lawyer in Thailand for more information if it does become complicated as a prenuptial agreement has to be registered together with the marriage registration.