Bangkok bank are usually pretty good. Try the branch in Thonglor if you're in Bangkok. And go with a Thai. You may need passport certification from British embassy too
They shd stamp for 60 and you extend at CW immigration before expiry in north Bangkok. Cost is 1900b. Maybe stay in a hotel the first night so you have an address for immigration, so your friend doesn't have to do tm30
Of course you can move here and get a non O marriage visa via the Thai embassy in your country first. Or come here on TR and get non O here. Lots of paperwork. You have to renew visa once a year in thailand plus 90 day reports .. and keep £10k in a Thai Bank account.