I don't have an answer for you, but you need to consider more than
just resolution. What is the total range of values you must handle?
Does it need to include bipolar, or only unipolar values? A 16-bit
bipolar system can handle a range of +/-32767 times its resolution,
for example. At 0.1uV resolution, you'd be able to handle +/- 3.2767
mV before overload. You should expect that you might
need a preamp to boost your signal so its range fits with the
range of the system, which will probably be something like 1V,
0.5V, 0.1V, etc.