baht last November when I got my Non O from London but that was for an Annual Multi-trip policy. I used a Thai broker/agent though the policy was with a European company. You could try messaging Arawan Namak.
I’m sure you’ll find her on Facebook. She usually replies quickly.
As they’ve been misused Ed visas will be a red flag to immigration and could lead to questions and hassle whenever you try to enter the country. I don’t know how long you hope to stay for? Remember you can stay for nearly 3 months on Tourist Visa.
You can extend for 30 days at any Immigration Office, it’s fairly straightforward.
You don’t need a return flight to get a Tourist Visa, an onward flight to a neighbouring country is fine. Whether they’d accept a flight to Singapore, I don’t know but the London Embassy is pretty good to deal with so it’s worth asking.
If you apply for a Tourist Visa they will want to see an onward flight (doesn’t have to be a return) out of Thailand and probably within the 60 days validity of the visa.
If you travel without a visa you are likely to be asked by the airline at check-in for proof you are leaving Thailand within 30 days. Again, doesn’t have to be a return flight just travel out of Thailand. You are unlikely to be asked for proof by Thai immigration.