Could you tell us the specifications of the filter you wish to implement? Both analogue and digital. Why?
Bandwidth - 1-3 Hz - OK. I presume -3dB points.
attenuation rate outside the passband in dB/octave.
Stopband attenuation.
Acceptable ripple.
Phase response.
Given that I may be able to suggest a solution. An analogue elliptic may be a good approach. What type does your digital filter implement? - given it's high order perhaps a Bessel....
is this an X-Y problem? ie are you asking a detail question on just a part of your perceived solution - which may not be optimal.
What does your overall project hope to achieve? There may be a better/easier way.
Allan