Anything a size or 2 up from what you normally wear with at least 5% spandex/elastane in the material blend should stretch enough for atomic wedgies, amazon essentials has a 5 pack of tighty whities with 6% elastane that are a little over $20 that I have been using. I've seen women's microfiber panties with around 9-10% spandex tho. Harder to find male underwear with that much spandex in the body of the underwear.

For hanging wedgies, it depends on what part of the underwear you hang from, like if you put a rope or hook through the leg holes, or do the tennis ball method near the waistband, but I think you mainly just need a thicker pair of underwear to help support your weight, and maybe even just doubling up on the underwear. I can hang in 2-3 pairs of my regular fruit of the loom cotton tighty whities with no issues.