I double checked the embassy website and called the embassy as well. They both said that showing a flight ticket to leave Thailand is required for who holds a 30 days visa exemption, for 60 days tourist visa holders the ticket to leave Thailand is not required :)
In that case, considering that I have a one way ticket already, what would be the cheapest option? A one way flight ticket to Laos or Cambodia to show that I'm leaving Thailand?
Do you think I can still apply for a 1 year multiple entries? It's a confused information on the embassy website but definitely I'll go to the embassy in London within 2 weeks for applying for 1 year multiple entries (possibly) or 3 months single entry, I'm just waiting for some documents prior