Sentinel-2 Level-1C use for NDVI

I am using the sentinel-2 products to calculate NDVI for crop cycle identification. I’m interested in the year 2016 but i could only find Level-1C data for this year in my area, which is Top of atmosphere data, so cloud cover is very high most of the time. There is no level-2A data for 2016.

Is there a way to calculate NDVI using level-1C ?! or Is there an alternative data set with the same resolution of Sentinel-2A ?!

You can simply calculate the NDVI on L1C. The result will be different when using TOA instead of BOA data. And the results will be more accurate with BOA data, but the effect is not that high, I think. NDVI is a ratio between two bands and by building the differences of the bands the atmospheric correction does not have a high impact on the NDVI. You could just try it and compare the results. If you do it, it would be nice if you show the results.
You could also try to fill the gap with Landsat-8 data.