A 220v inverter will not use any more power than a 110v inverter.
As others have said many appliances
are muli volt so it is usually cheaper to shop for appliances
that can operate on the voltage of the inverter.
There is a big difference between the real world efficiency of inverters.
Generally the smaller inverters that will still run the load are better, but their are considerable differences between brands/models.
Have as much as possible running from 12v directly is the best option. There is not a lot used on the average cruising boat that cannot be run from 12v.
At least try and have commonly used items direct from 12v if you want maximium efficiency.