Just bring a blue ink pen (very important) 2 passport photos, fill out the paper work at the Sotomor (Chaeng Wattana), get a number go buy a coffee then go see the immigration officer and pay ฿1,900 THB
I personally go in the afternoon around 1300 hours since I’m not a morning person, they are open until 1700 but will stay until the last person is seen with a valid Queue number…
Super simple no need for an agent…unless you want to waste the agent fee