I agree with Barmaglot, the Son RX100Va would be a great step up, If you want an interchangeable lens camera that is a step up I would recommend the Olympus EPL-9 or -10. You can use the 14-45mm kit lens with wet lenses and then when you decide to step into a dedicated macro or wide angle lens you can get the specific lens and port. Take a look at the backscatter website for the Olympus EPL10.
I've upgraded from the Sony RX100Va (available for sale with housing) to the Olympus EPL10. Feel free to PM me any questions you have about either the RX100Va or the EPL10.