Hi Smokestack! The Referee's Manual has an alphabetical list of monsters by area types on pages 112-117. If I wanted Dungeon/Subterranean, I'd break that area list down into hit die groups using Blackadder23's monster list by hit die, then roll depending on what level I needed. For example, you could construct a simple list of ten Level 1s that you like and roll a d10 or, for more challenge variety, maybe drop a Level Two in for slots 8/9 and a Level Three in for slot 10. Most of the time you'd get a "level appropriate" encounter, but once in a while, you'd get something more challenging that might require running away instead of fighting.
Hope that helps and also hope to hear about your campaign in our Campaign forum, whether it's a written or YouTube recap.