I’m starting out as a somewhat overweight 61 yo. Just got my first real TREK (Marlin 7-2021) and started commuting as a way to work out. I’ve done ‘some’ minor trails but barely beginner stuff. The one key to comfort is all the contact points as one being our seats or saddles. I can’t tell you which is best for you and that may change as you get more fit. My stock saddle is fine for now as I’ve done only a few 5+ milers with breaks (my youngest son takes a lot of breaks while riding.) along the way.
From all that I’ve read and YouTubed, getting the right saddle for you is key to comfort. Also getting ‘sized’ for one’s bike is important. The wrong geometry and you will always be miserable no matter how good your physical status. Your local Trek shop should be able to help and there are loads of YT vids to watch along this line. Good luck to both of us in our getting healthy and MTB adventures. I’m jealous of your Roscoe already but I’m loving my M7.