Actually if you are retiring at 65, you and wife can choose the CPF Life Enhanced which will give you and wife $4k pm in total. Assuming you are debt free and your home is paid up, $4k pm should suffice for food, utilities, public transport, medical, etc.

If you're retiring earlier at 55, you must be a high flyer who have assets that can produce at least $5k pm for you and wife. This also assumes you're debt free by 55.