Is it permissible to suffice with the istikharah (guidance-seeking prayer) of the woman who found much good in completing the marriage, despite the man's lack of comfort or his heart turning away from the matter?

If the means for marriage, for which Allah has been consulted (through Istikhara), become available, and your heart does not turn away from it, then do not hesitate. Resolve the matter and rely on Allah, for the hadith does not stipulate a feeling of contentment (in the heart). Your Istikhara is a sign of your happiness, and the Istikhara of others cannot replace it.