DEM generation of tidal flats using InSAR


I am trying to generate a DEM of an intertidal area (tidal flat) using InSAR approach. These areas are subject to tides (covered in water at high tides and emerges at low tides). I am trying to generate interferograms using two acquisitions at low tides. Due to the important changes in the flats conditions (especially from the soil moisture and the temporal baseline), my interferogram is heavily decorrelated. That’s obvious in my coherence results.

I searched in the literature and I found dem generation from single-pass InSAR. But in my case, I am using Sentinel-1 data repeat passes.
Does someone have some experience in using InSAR in these areas? Is there a way to improve my coherence? Is there free single-pass InSAR data that I can use?