We will be arriving for 3 months in early January with a 90 day non-immigrant Visa. Does anyone know the procedure for an extension on this as our arrival and departure from Bangkok is actually 105 days. We will be travelling to Hong Kong in February for 7 nights and also Singapore and Kuala Lampur at some point in our stay.

Is there a better Visa system for us to use? Our base will be in Koh Samui for the three months.

A visa only allows one entry - once you depart Thailand you no longer have a visa to come back with. You can pay 1,000 baht to keep your current permitted to stay alive for a short trip but if you are from one of the 40 countries permitted to stay without visa for 30 days that might be a better option. Use visa for January entry. Obtain 30 days on return in Feburary and the same on return from Singapore and/or Malaysia. Just time your travel so that no more than 30 days inside Thailand each time.