Consider using the standard 3 op-amp differential amp circuit. This will provide the high impedance inputs you require and you can change the gain using a single pot rather than a dual gang pot.
Using a dual gang pot to change the gain of a single op-amp differential amplifier is not a good idea as you will never get good enough matching between the elements of a standard dual-gang pot to maintain good common-mode rejection over a wide gain range.
So basically an instrumentation amplifier? Because I'm currently looking at the INA851, which has a differential output, as well as a V
OCM pin (required for my ADC). This one IC can be the entire input stage for my application. It's a bit expensive, but it replaces multiple components so it might even pay for itself. The only concern I have is if I can find a potentiometer with a reasonable taper for my application. I need a gain from 0.5 to 600, which corresponds to a resistance between 4k and 2 ohms.
A linear pot would result in a very skewed scale. This chart is already logarithmic.
Using a reverse logarithmic pot helps, but it's still pretty inconsistent.