Ladies and Gentlemen:
A larger, plumper, cushiony saddle is not going to help you if seeking relief after your first big bike ride. There is no remedy. You can't buy your way out of this problem!
What has happened is the nerves in your sit bones are badly inflamed from the chronic pressure of your long ride. That inflammation is going to hurt to the slightest touch, whether it's a luxurious saddle or a plank of wood.
DO NOT run out and spend cash on any saddle that is advertising "comfort" or "relief". What you need is a proper road saddle, that is selected to align with the width of your sit bones.
Here's the deal. Have you ever pinched the skin on your elbow? Do your elbows hurt when resting them on a hard table? Not likely. This is because chronic pressure on the elbow in the normal course of life has killed off all of the nerves.
Now we begin to see the real antidote to saddle suffering. It's habit. Ever wonder how professional riders can go 6+ hours in grueling bike races without pain or complaint? Its all a matter of riding frequency. Pros ride 20+ hours a week. Their sit bones are exactly like their elbows.
All of this to say, saddle pain does go away over time, but you must choose the correct narrow saddle for your body, and ride, ride, ride lots. On a long enough timeline (lets call it anywhere from 15 to 25 rides in a 20-30 day period) your butt pain will dissipate! Not 100% but enough that you will feel "at home" on your bike saddle.
A pair of padded cycling shorts also alleviates pressure and friction (no underwear! that defeats the purpose!) and using a balm to make your shorts "stick" to you is also a good habit. (This eliminates friction inside of your shorts, so that the friction ends up on the outside, against the saddle) Choose a saddle with a slick smooth finish too, you dont want any "stickiness" to your shorts, you want to slide fore and aft freely.
And for those concerned with genital numbness, most people find some relief by tipping the nose of their bike saddle downward a few degrees. It's a matter of trial and error, but you'll find that sweet spot. There are saddle available with a relief opening down the center. These are also a good remedy.
Saddle height also plays an important factor. If your saddle is set too high, there will be more pressure on your crotch than necessary. You know your saddle is too high when your hips rock slightly while pedaling. A saddle that is too low may not hurt your butt, but it will hurt your knees. Generally speaking, when your foot is at 6 o'clock, your leg should be extended 90%, a slight bend at the knee.
Knee pain is a reliable marker of saddle height mistakes. Too high will give pain in back of the knee. Too low will produce pain at the front of the kneecap.
Handlebar height is often overlooked. The casual bike rider seems hell bent on having their handlebars as high as a Hell's Angels HOG. This is incorrect. What a upright bike position does is put the majority of your body weight on your bum. You are basically falling through the ice while trying not to slip.. Lower handlebars help you two ways. First, a low position distributes your body weight more evenly between butt and hands. Secondly, when your weight is successfully distributed with a lower handlebar, your control of the bike is enhanced, especially when cornering through a turn. You think your back will hurt from bending over but the reality is that your hands, arms, shoulders and trunk give your back the support it needs.
Now ride way more so that those sit bone nerves adapt!