If you break the law of overstay and don't get it cleared before you go to airport then you will be banned by airport immigration... there's no reason for anyone to be on a overstay before arrival to airport... check the law before doing the crime..always clear any overstay before leaving the country....or you can get a 5 year ban for a 5 month overstay.
You don't need a agent if you got the money in the Bank.. practically easier paperwork for you than you did for your gf first visa to the UK ..your get everything you need by contacting the Thai embassy London ...
I am a single dad daughter nearly,18 son 6 years..i don't do bloggs to make money everything I do in chonburi and information I give out is free..respected for helping Thai and foreign people....i am messaged frequently for advice...i dont need to be a know it all. I do what I do for charity and the good of the community at my own costs not making money from you tube . thanks for your reply..regards Glenn