Wider saddle doesn't always make things better. It can make things worse for some. How I avoid saddle soreness on >1 hr trainer rides is doing intervals. Doing the same resistance and same cadence for over one hour is sure recipe for saddle soreness. Low resistance and high cadence spinning have a tendency to cause saddle soreness so you need to break it down into segments.
I usually divide in 20 minute intervals or less. 20 minutes high cadence spinning on low resistance, followed by 20 minutes lower cadence at higher resistance, and repeat if you wish to train for longer period. You can also stand from time to time going several pedal revolutions before sitting back.
Also no underwear. At least I don't wear one when training or riding. Seems to cause chaffing and I like to feel as ventilated and cooled as possible.