@Natalie *******
Every embassy and consulate has their own rules. For example, the OX visa (5+5 years) is the longest term retirement visa, but because it requires $150,000 (Aus dollars) to be placed in a Thai bank account, not many people apply for it. However, the Sydney consulate will accept that amount held in an Australian Bank or Super Account (the only consulate in the world to do so), so the OX is becoming very popular with Aussies. It's a ten year visa, and is a fraction of the cost of an Elite Visa for the same period.
Yes for your particular circumstance, probably ED visa is the go. The retirement visas are more for people wanting to stay much longer term in Thailand.