Herein, a sensor system was developed for non-contact electrocardiogram (NcECG), non-contact diaphragm electromyogram (NcEMGdiaph), and NcEMGdiaph-derived respiratory variation (NcRVEMG) measurements that use sheet-type fabric electrodes placed under a subject in a supine position. We developed prototype system was evaluated with both adult and infant subjects. In a basic evaluation test on the adult subject, we confirmed that the reference respiration rates and the NcRVEMG signals were highly correlated (r = 0.96). Tests with three infant subjects confirmed that the prototype system can simultaneously measure the NcECG, NcEMGdiaph, and NcRVEMG signals. In these tests, the proposed system exhibited improved sensitivity by 19.7% and accuracy by 10.5%. These results suggested that the developed prototype system can measure the NcECG, NcEMGdiaph, and NcRVEMG signals in infants during sleep or at near-complete rest.