Usually, the most reliable wave data for any of these areas come from the Wavewatch III solutions. Either the global solution or the one for specific regions (there is an Indian Ocean solution). The data is available at the NCEP site (https://polar.ncep.noaa.gov/waves/validation/gefsv12/). In terms of what the right metric is for wave height, significant wave height (the average wave height of the top $\frac{1}{3}$ of the waves during a specific sample time) is the standard metric used in almost all applications related to wave dynamics.
If you are interested in climatological data from the area, I think your best chance is the paper by Anoop et al. (2015). It describes average wave height fields, but also the tendency over the last few years. Directly from their paper:
(left) Mean swell and (right) wind sea height in the NIO by wave energy statistical method: (a) annual, (b) premonsoon [February–May (FMAM)], (c) monsoon [June–September (JJAS)], and (d) postmonsoon [October–January (ONDJ)]. All values are in meters.