Tires. PSI. Saddle. Fit. Posture. All these can be tweaked before you need to think about a new bike.

As others have said wider tires and slightly lower PSI might help, but don't soften the tires too much or you'll be at risk of pinch flats.

It takes a while for a butt to get used to a saddle. Also if the saddle just doesn't work for you, a new saddle is better than a new bike. Soft saddles in some ways are worse than hard saddles because your butt bones (ischial tuberosities) sink into them and your soft tissues end up carrying more of your weight. It's better to have a firmer saddle, and get your bony parts used to it.

Fit and posture: Ideally your weight is carried by your butt, feet and hands, all sharing a portion of the load. Too much weight on your butt and it hurts. Too much weight on your hands, and you may get a wrist injury, like carpal tunnel syndrome etc. Your seat should be far enough back that your feet are below your centre of gravity, like a swimmer poised to dive, with his butt sticking back. If your seat is too far back, it's hard to reach the brakes, but if it's too far forward it makes you lean too hard on the handlebars, so make sure you research your fit or have a shop do it.

When you pedal, your legs naturally tend to carry some of your weight, but also when you coast, try to keep some tension in your legs or even stand up from time to time to relieve your butt.