I am in a somewhat similar situation (single, almost 61, modest non-cola pension, SS soon). I've backed of a little from 55/45 to 50/50 recently. Like many have posted, I would not feel comfortable at 20/80.
FWIW - My Vanguard Flagship Rep also thought/suggested that 50/50 was a good allocation for me. Maybe they are just using the "new" 110-age rule. Don't know.