Ketamine is not a promising drug – please see the following article published in The Lancet Psychiatry:

Turner, E. H. (2019). Esketamine for treatment-resistant depression: seven concerns about efficacy and FDA approval. The Lancet Psychiatry, 6(12), 977-979.

I also do not think it is necessary to mix drugs with mindfulness, especially considering that Mindfulness is a skill (like any other skill such as playing the piano or learning to swim) that can be gradually developed with continued training – one wouldn’t want to take a drug to improve one’s piano playing..