We have estimated the bulge-to-total (B/T) light ratios in the K(s) band for a sample of 24 S0, S0/a and Sa galaxies by applying a two-dimensional multicomponent decomposition method. For the disc an exponential function is used, the bulges are fitted by a Sersic R(1/n) function and the bars and ovals are described either by a Sersic or a Ferrers function. In order to avoid non-physical solutions, preliminary characterization of the structural components is made by inspecting the radial profiles of the orientation parameters and the low azimuthal wavenumber Fourier amplitudes and phases. In order to identify also the inner structures, unsharp masks were created: previously undetected inner spiral arms were found in NGC 1415 and marginally in NGC 3941. Most importantly, we found that S0s have a mean < B/T >(K) ratio of 0.24 +/- 0.11, which is significantly smaller than the mean < B/T >(R) = 0.6 generally reported in the literature. Also, the surface brightness profiles of the bulges in S0s were found to be more exponential-like than generally assumed, the mean shape parameter of the bulge being < n > = 2.1 +/- 0.7. We did not find examples of barred S0s lacking the disc component, but we found some galaxies (NGC 718, 1452 and 4608) having a non-exponential disc in the bar region. To our knowledge, our study is the first attempt to apply a multicomponent decomposition method for a moderately sized sample of early-type disc galaxies.