Bike shorts are totally designed for no underwear. Another thing that helps is "chamois butter", a sort of lubricant/ moisturizer for the crotch. Our gracious hosts Team Estrogen sell the stuff, it's great. Vaseline works well too, but isn't water soluable and can get messy. The quality of the shorts makes a big difference too. You want flat fell seams in cycling shorts, not regular seams that make a lump. And the padding should be decent, don't use cheap shorts with fuzzy fleece stuff. The fibers are basicly plastic and will chew your skin off. You will be incredibly happier with tampons.
Seats- as a huge fan of Terry saddles, I encourage you to look at the website. (Look at the shorts, too) That hole in the middle is what we like, it takes the pressure off the sensitive bits. If your bike didn't come with this feature, you can get a $25 or $30 saddle with springs if you want'em and more padding than the Terry. I ride hundred dollar Terry racing saddles, but if you're at the twenty mile stage that may be overkill when you can get a good knockoff. I have a $25 Avenir on my city bike that I love. It's pretty normal for a rider to go through a few saddles to find what they like, and as you go longer distances you'll want firmer pricier performance saddles. More upright bikes have wider back ends, as you lean over more you tend to want a narrower seat. Generally.
Actually, the lower end Terrys like the original Liberator may suit you too. You know where it hurts, and should look at some different saddles and see whats available. You can probably tell what you need. If the saddle is even a problem. I'd ditch the undies and get some chamois cream and see how it goes.

missliz