OPs "bike" is an air assault style stationary bike.
I am not sure any typical bicycle saddle recommendations will work for this sort of device.
Edit: Oops came to the thread after a coupe hours of it being up and I see this has been addressed.
@Sanch you need to continue to mess with your saddle positioning and I bet you will be able to find a position where the numbness does not occur. Lower the nose, make sure the saddle is not too high, nor too far back.