Only one? That’s a tough choice. I think I would want to talk to Our Blessed Mother. I think she would be the most reassuring and comforting one to talk to. And I could ask her if people I knew were in Heaven.
If Mary doesn’t count then I’d request St. Joseph. He seems to be the most helpful and reassuring after Mary, but people seem to forget him. Last year I did this Pro-life Rosary at a church and at the end they did a little impromptu litany of saints including the patron saint of the church we were in, Mary, and a bunch of other saints and apostles, and totally forgot St. Joseph. They asked for suggestions from the group so I of course said him right away. I’d like to know how he coped with everything.