Great thoughts, Steven! I must confess that I'm not as well-read on this subject as I ought to be. I'm familiar with more work than I've had time to sit down and read myself. But I'll recommend The Great Divorce and The Last Battle by C.S. Lewis, as well as God Can't and God Can't: Q&A by Thomas Oord. Those books aren't specific to Universalism, per se, but they've profoundly shaped how I think about God and the afterlife. I listen to many Christian podcasts that have done episodes about the afterlife, including The Deconstructionists, The Bible for Normal People, and Tim Mackie's stand-alone podcast, Exploring My Strange Bible. If you browse their catalogs, you'll find several relevant episodes. Bradley Jersak and Rob Bell, of course, have also written about Universalism.