RC Lowpass Filter between Amplifier and ADC input
If you are reading the ADC just once per second then you need to eliminate frequencies above 0.5 Hz to prevent aliasing. If you think your system will have noise at, say 10 Hz, then that noise will contaminate your readings. I recommend that you sample at a much higher rate, perhaps some multiple of the power mains frequency, and perform low-pass filtering in software. Even a simple moving-average filter would work and wouldn't take much processing.