Physical Water Surface

I’m still struggling with reflections in forward shaded mode, as planar reflections are too expensive, but even reflection probes don’t seem to work either as I can’t see any clouds even in a fairly calm physical water surface:

I recently saw this technique which uses a pre-rendered cubemap and I’m wondering if it can be adapted to this water material, at least to reflect the surroundings even if it probably can’t work to reflect boats: