Know that ATMs will cost you quite a bit! Usually, the fee is around 220 Thai Baht for each withdrawal. ATMs will levy the same fee, excluding AEON, which is somewhat more reasonable at 150 Baht.
However, on the downside, AEON ATMs are hard to come by and are usually found at local shopping centres away from downtown Krabi. To limit withdrawals, take as much cash as possible, and store them in the hotel safe.