Hi Tanya. No only the completed arrival card handed out on the plane is needed. Jeremy mentioned a TM30 form above, but he meant the arrival card. TM30 is just to register your address for people staying in private residences (ie not hotel).
An IDP is only valid for 90 days for insurance and is not designed to be used long term. Repeated IDPs while living in Thailand is not recommended. Should go for the Thai licence.
Are you in a hotel or residence? They seem to be clamping down on this TM 30 thing in some places....probably mostly in Pattaya though.....catching a lot of people out recently if Landlords don't register you.