I wear normal underwear and athletic shorts when I ride. Same inside and out. Being on the trainer is definitely different so maybe I need specific biking shorts for that. I tried some padded ones but I think they were too big because they rode up really badly. What do you look for in a good pair?
I like the idea of standing up for a break occasionally. It's completely flat here so I rarely stand on a bike but this morning I tried it outdoors for a couple hundred feet after about 35 minutes of biking. I think it helped. Standing on the trainer felt really awkward but next time I'm on it I'll try again. Thanks for the good idea!