A couple of ideas: one, a lot of bike shops have loaner/trial saddles, or some type of policy where if you don’t like one in the first month you can either return it no-questions for a refund or store credit (which you can turn around and use to try a different saddle). If you can’t take a loaner on a long ride, at least try it out the day after a long ride when you’re sore and tired.
Two, and this relates to your hands as well: the more tired your legs get, the less you push on the pedals and the more weight your butt and hands are taking. Getting tired is inevitable, but Any way you can postpone that will help, whether that’s stronger legs, more frequent position changes, more breaks taken completely off the bike mid-ride, doing something different on descents when coasting. (I stand on short descents a lot, myself, or do the silly sounding but useful option those of us with a fair bit of inner thigh fat have of sitting on our thighs—can’t pedal that way but it gets me off my butt here and there.)